Or, (forgive the speculation) Could the mythological group be the result of a sort of Late Bronze Age version of the children's game Telephone talking about the Denyen, with just enough mis-hearing of the name to get to the mythological group?
The etymology of Danann is ambiguous, but it is not attested before the later medieval period in Ireland. The earliest texts make reference to the Tuatha Dé 'tribes of the Gods' or the Fir Dé 'men of the Gods' instead.
The common hypothesis is that it became necessary to distinguish the pagan gods from the Tuath Dé 'tribe of God', which is to say the Israelites...not groups you want to be confusing in a monastic setting. Though why Danann (earlier form Donann) specifically was affixed for this purpose, is not known for a certainty. Eochaid ua Flainn, whose poetic work forms part of the Lebor Gabála Érenn, vaguely glosses the name in a bit of slightly incoherent verse:
Heriu cid rotbla roa,
Banba, Fotla, ⁊ Fea,
Nemaind na forand fathach,
Donand, mathair na nDea.
Eriu, whatever haven [?] she may reach,
Banda, Fotla, and Fea,
Neman of the . . . ,
Danann, mother of the gods.
However John Koch notes there are no earlier traditions associated with such a figure, and the word itself is "indeclinable", suggesting it is perhaps a construct (or corruption):
Noting the term's problematical character, L.C. Stern suggested that whoever added the third element did so by conflating the name of the trí dé dáno (three gods of skill), a mysterious group to which there are several allusions in the literature, with that of the land goddess Anu (genitive Anann), called 'mother of the Irish gods' by Cormac ua Cuileannáin and often identified with Donann in later sources. Stern's persuasive argument leave only the -o- of the first syllable un-accounted for. As the present writer has tentatively proposed, the ethnonym Domnann might have exercised some influence here.
John T. Koch. "Tuatha Dé." Celtic Culture.
Referencing: Ludwig Christian Stern. “Ein ossianische Ballade aus dem XII. Jahrhundert.” Festschrift Whitley Stokes zum siebzigsten Geburtstage am 28. Leipzig: Otto Harrassowitz, 1900. p. 17
In any case, the status of the Tuatha Dé as preserved pre-Christian 'Immortals' (which Koch calls "the least inadequate" label) is uncontroversial. Certainly their significant connection to the landscape via the ancient monuments and barrows seems to be long-standing. Invasions were a common literary device in the medieval pseudohistorical tradition, so the appearance of that motif in a synthetic history like the Lebor Gabála Érenn is not necessarily indicative of any historical basis.
If I seem to be stepping around the question specifically, it is because I have never heard of the 'Denyen', nor of any proposed connection between them and the Tuatha Dé, so cannot respond to such an idea in detail. However there is no evidence that I am aware of, linguistic or otherwise, to support such a connection.