You're quite right, there isn't much evidence of any sort of Norman bond between what I generally refer to as the northern and southern Normans - that is, the Normans of Normandy, Britain and Ireland under William the Conqueror and his sons on one hand, and the Normans of southern Italy and Sicily under the Hautevilles on the other. There are undoubtedly sub-divisions within these categories (between Normandy and Britain, Britain and Ireland, Italy and Sicily, Sicily and Antioch, etc) but the north-south distinction is the big one.

I've touched upon parts of this elsewhere in /r/AskHistorians but I'll reiterate some of it here. There are a couple of key things to bear in mind about the southern Normans: firstly, that their relocation from Normandy to the Mediterranean was neither ordered nor sanctioned by the Duke of Normandy, and thus was not an official 'Norman' action; secondly, that once the first wave of Hautevilles and their companions settled in Italy and Sicily, successive generations were born there and probably never set foot in Normandy.

The significance of that first point is that unlike the conquest of England, the exodus to Italy was independent. It wasn't expansion of Norman territory, it was a relatively small number of people who happened to be Normans taking action on their own account to improve their future prospects. To quote myself from another topic,

Tancred de Hauteville couldn't support all of this sons in a suitable manner and there was nothing much for them to look forward to in terms of social standing or what we'd now call 'career' - 'their own neighbourhood would not be big enough for them' and 'individual shares [of their inheritance] would simply not be big enough' (Geoffrey Malaterra, The Deeds of Count Roger of Calabria and Sicily and of Duke Rober Guiscard his Brother, trans. G. Loud). Robert Guiscard and his kin went to Italy to seek their fortune, to try and carve out some sort of meaningful and productive life for themselves. They had initially fought alongside the Byzantines and then turned on them to capture Byzantine cities in southern Italy as soon as it became practical to so, culminating in stamping out the last of the official imperial presence with the conquest of Bari in 1071 (Oldfield, City and Community in Norman Italy).

Rather than being a Norman expansion, it was just the disillusioned sons of a minor noble rounding up their friends and heading to far-flung lands in search of riches. As such, there was nothing much tying this endeavour to the rest of the Normans. If anything, we could imagine (though this is conjecture) that the Hautevilles felt no particular loyalty to a duchy and duke that had left them in such penury that they had to take matters into their own hands. It's hardly surprising that this circumstance did nothing to foster a sense of Norman brotherhood between the southern adventurers and their peers back home.

That's the first of the two points I mentioned before. The second point, settling in Italy/Sicily and having children there, is equally significant in my view. If I can momentarily be indulged in some anecdotal evidence (real evidence will follow shortly, I promise) I have a friend called Adam whose parents are both English; they lived most of their lives in England but then moved to Wales some time before Adam was born. He, then, was born in Wales, was schooled in the medium of Welsh, and is a bilingual English-Welsh speaker. He considers himself Welsh. The fact that his parents are English is irrelevant; he is Welsh. This is dealing with two countries that are immediate neighbours - imagine the shift in national identity when the Normans who went to Italy had children there. Would the children consider themselves Norman or something else?

On to the real evidence then. Again, to quote myself (in order to spare my typing fingers),

Dr Mark Hagger remarks that 'by the early years of the twelfth century, however, the first generation of Italo-Normans ... were referring to themselves as sons of Normans' (Hagger, 'Kinship and Identity in Eleventh-Century Normandy: the Case of Hugh de Grandmesnil, c. 1040-1098', Journal of Medieval History 32).

That fits with anecdotal idea above. More concretely, we can turn to the diplomata (the official documents - writs, charters, etc) of the Hautevilles in Italy and Sicily to give us an indication of how they thought of themselves. Again, from me,

Once you head into the 12th century the diplomata of Roger II and William I just don't mention the Norman connection at all. Where the diplomata of, say, William the Conqueror in Normandy describe him as dux Normannorum (duke of the Normans) the diplomata of Roger II and William I use terms such as rex Sicilie, ducatus Apulie and principatus Capue - king of Sicily, duke of Apulia and prince of Capua respectively (ed. Enzensberger, Guillelmi I Regis Diplomata).

The last couple of quotes come from a more detailed analysis of Norman identity in southern Italy and Sicily in this thread. You might find that thread useful if the Normanness of the southern kingdom interests you. If you have access to academic journals, I'd also recommend Graham Loud's article 'How "Norman" was the Norman Conquest of Southern Italy?' in Nottingham Medieval Studies 25.

Of course, sense of Norman identity is only one aspect of this question. The other main aspect, I'd contend, is whether there was much contact between these two realms. At this point we're getting into muddier waters. There's little indication of any more contact between the Normans of Britain/Normandy and those of Sicily/Italy than would be expected between any other two monarchs. In 1177 William II of Sicily married Joanna, a daughter of Henry II of England (Houben, Roger II: a Ruler between East and West) but this is over a century after the Hautevilles' departure from Normandy and three generations have called Sicily and Italy home by this point, so I don't think we can attribute any significance to it beyond a marital alliance between two powerful rulers.

There's a bit more murkiness in the composition of the courts which might suggest a more persistent connection, but it hasn't been researched in much detail. I'm thinking of influential individuals who served at court in Sicily, England and/or France. Stephen du Perche, for instance, was a son of the count of Perche in France (Hugo Falcandus, Liber de Regno Sicilie, ed. G.B. Siragusa), served as chancellor in Sicily under William II and had a brother called Geoffrey who was named as witness to several of Henry II's charters in both England and Normandy (Graham Loud's footnotes in The History of the Tyrants of Sicily by Hugo Falcandus 1154-69).

There were others too. An Englishman named Richard Palmer was a very prominent individual at the Sicilian court for a number of years, acting as both Bishop-Elect of Syracuse and a familiaris regis (a close, trusted advisor) to more than one ruler of Sicily. It's not clear whether Palmer ever served one of the kings of England but it's certainly plausible. The letters written by Peter of Blois place Peter himself both at the royal court in England and in a prominent position of influence in Sicily (ed. & trans. Loud, Some Letters of Peter of Blois Concerning Sicily), plus he was of French origin. That makes three I can think of offhand, and I'm sure there were others who currently elude me. Personally I tend to think Peter of Blois fabricates a lot of grand claims to impress his friends, and his claims are unsubstantiated by other sources, but certainly Richard Palmer, Stephen du Perche and maybe a few others had connections on both sides. It might be nothing, but I'd be remiss in not pointing it out.

It's worth noting also that many of these potential connections between England/Normandy and Sicily occur during the reign of William II of Sicily, long after the Hautevilles parted ways with Normandy and after a long period of little evidence of any such ties. For that reason if no other, I lean towards the view that any ties between England/Normandy and Sicily during William II's time were new creations and resulted from the overlap of notable officials rather than causing it. That's just my opinion though; as I said, I don't know of much research devoted to that topic. Hiroshi Takayama is probably the historian to look up if you're interested in the powerful officials of Sicily.

That might be a longer and more convoluted answer than you were looking for, but it's a very unclear area. 'Absence of evidence isn't evidence of absence', as they say. As with so much that relates to the Mediterranean Normans, a lot of it comes down to balance of probabilities based on limited evidence.

Before I wrap up here, I know I haven't touched on Ireland or Antioch, with good reason. I know effectively nothing about Norman activity in Ireland so I'll have to leave that to someone better versed in the topic. Antioch is a bit closer to my field but it's not one of my prime interests. The Normans who ruled Antioch, Bohemond I and II, were the son and grandson of Robert Guiscard (one of the first wave of Normans to settle in the south) so there's that connection, plus Hubert Houben reports that Bohemond II left someone to rule his Italian territories while he was away, so it's clear that Antioch was very much connected to Italy. Additionally, when Bohemond II died, his cousin Roger II of Sicily tried to claim Antioch for himself on kinship grounds (Houben, Roger II: a Ruler between East and West), which points to the other southern Normans seeing a strong connection between their realm and Antioch thanks to the Bohemonds. Antioch was never really settled by Normans in the way that Italy and Sicily were though, so I consider it almost more of an outpost than a realm of its own.