Was it common for wives of noblemen to accompany their husbands on campaigns?

Although we don't have the data to say how common it was, it generally wasn't seen as abnormal. There were usually two choices regarding what a medieval wife would do when their husband went off to war, assuming they played an active role in their life (many medieval marriages were ones of politics more than love, so couples were not always minded to actually do stuff together).

Option one was for the wife to stay behind and take over the administration of their lands. Option two was to go with him. For example, when count Baldwin IX of Flanders set out on the Fourth Crusade, his wife Maria stayed behind for two years to run the county, then decided to join him on the crusade. Unfortunately, she died of illness when she got there. When king Louis VII of France set out on the Second Crusade, his wife Eleanor of Aquitaine joined him, though the crusade led to the breakdown of their marriage. When Eleanor remarried to king Henry II of England, she often accompanied him too. It was down to the personal preferences of the couples involved, but the presence of the lord's wife in a military camp was certainly nothing unusual.

Did they ever participate in combat?

This is where it gets interesting. We know that there were female military commanders, and although knighthood was an exclusively male institution, there was nothing to stop a wealthy woman from buying a horse, some armour, some weapons, and fighting like a knight. Women could, through inheritance, become lords, and as lords they could maintain a retinue of knights that they were legally entitled to lead. On the Second Crusade, Eleanor of Aquitaine invoked her status as duchess of Aquitaine to command her own contingent of knights. It didn't go very well, as Eleanor was young and inexperienced, so deputised to impetuous lieutenants who deviated from the battle plan and got a lot of people killed by doing so. Another famous noblewoman of the Middle Ages was Matilda of Tuscany, who defeated the Holy Roman Empire in battle on behalf of the papacy, and forced the emperor to walk barefoot through the snow begging for forgiveness for his sins. She was known to don armour and charge into battle with her knights. Women could, under the right circumstances, be respected military leaders. It was also recorded by some sources, Greek and Muslim, that handfuls of crusading knights were actually women in male garb. For example, when writing about the Fourth Crusade, the Byzantine civil servant Nicetas Choniates noted that

Females were numbered among them, riding horseback in the manner of men, not on coverlets side-saddle but unashamedly astride, and bearing lances and weapons as men do; dressed in masculine garb, they conveyed a wholly martial appearance, more mannish than the Amazons.

It is exceptionally rare to find a mention of women fighting in the Middle Ages without them being compared to the Amazons; the famous warrior women of the Homeric epics, which brings us back to Guiscard and Anna Komnena. Whether women should (or even could) fight was a topic of debate, and the argument in favour centred on "historical" examples. The Amazons were one, the idea of shield maidens in the Germanic armies of late antiquity and the early middle ages were another. They also looked to classical authors such as Aristotle and his comments on Spartan women.

It wasn't a popular view in an era that was intensely patriarchal and misogynistic, but there were those who were happy for their wife to take charge and fight. Robert Guiscard was one of them. His second wife, Sikelgaita, is the one mentioned by Anna:

There is a story that Robert’s wife Gaita, who used to accompany him on campaign like another Pallas, if not a second Athena, seeing the runaways and glaring fiercely at them, shouted in a very loud voice, ‘How far will ye run? Halt! Be men!’ – not quite in those Homeric words, but something very like them in her own dialect. As they continued to run, she grasped a long spear and charged at full gallop against them. It brought them to their senses and they went back to fight.

Anna likes to frame everything as if it's straight out of Homer, but the basic fact that Sikelgaita led Guiscard's army in his absence is well attested. She even decided to take the title of duke rather than duchess, which had more military connotations, depending on the situation. When giving a donation to a monastery or church she was a duchess, but in castles she was a duke. It's not clear how often she was actually on the front line, since she was not under the same pressure to put themselves in mortal danger as men were, and she was quite far into her middle age by the 1070s and 1080s when her military activities were at their peak.

So, it wasn't common, but it also wasn't seen as wrong. Women could command if they held a title, and a noblewoman could lead in person if they wished.