Since it's known that when Ragnarok occurs, all of the fallen vikings who weren't worthy of Valhalla or folkvangr are sent to helheim to eventually be led by Fenrir to destroy Odin and all of the Aesier, then why would Odin allow for more men to be equipped to his ultimate demise? Is it because he knows he will eventually die anyways from it, regardless if he hinders Fenrir or not?
When Ragnarök is described in Völuspá (stanza 34 and on) and Snorri's Edda (Gylfaginning, 55-56), there is very little said about those that are with Hel. The closest we get is that we are told that the ship Naglfar, which somehow is important for Ragnarök, is made from the nails of dead men, but there is no further specification of whom it will carry.
Furthermore, when we get a glimpse of the reborn world in Völuspá (stanza 59 and on), we see that one of the Aesir that inhabits this new land is Baldr, one of the few people we are explicitly told has gone to live in Hel.
Thus, I see no reason to suppose that the dead in Ragnarök will join the battle, unlike the various giants and monsters we are told will be there.