The thing I’ve seen most of among Osttruppen in Normandy from photies — probably helped by how bulky and distinctive in appearance it is — is the good old PM-10 Maksim. If you’re going to have a bunch of those — and I seem to recall Ostbattalionen often retained Soviet-style organisation, so you might have nine of them in the MG Coy — then it probably costs little more, in logistical headachery, to provide everyone with rifles in the same calibre. the same might be said of LMGs, though I don’t recall seeing any DP-28s in photographs from Normandy. SMGs, though, are a bit different, as they don’t contribute a fantastically large proportion of the unit’s firepower, and fire a cartridge shared only with pistols, which are essentially status symbols for officers.
During the course of my googleage I have seen this same question asked in a couple of other fora, and nobody seems to have produced any definitive photographic or documentary evidence yet.
All the best,