You can recruit both of the units, the new recruits article is very specific on that point. Ex: "The Obscene is a bloated, disgusting abomination that gorges itself on the flesh of the fallen, its cannibalistic atrocities demoralizing all who look upon them. With an initiative rating of four, these bulbous warriors can be recruited as an alternative to the mighty Chaos Lords, but the most effective armies will include one of each."
Good quote, there:) I don't see any of the new units making any of the old obsolete. As previously mentioned, the key to tactics in Runewars is adaptability. Players committed to a certain troop type or strategy will be handicapped when certain circumstances arise. Similarly, smart players will begin to pick up on redundant Recruit picks, etc., and respond to that threat. What these new troops offer is a chance to resist becoming predictable. As an Elf player (for example), the ability for Waiqar to pick Vamps over Necros will lead me to reconsider how many Archers I take into battle vs. Waiqar, where before it was simple. I skipped the Sorceress and went heavy with Archers/Warriors.
Runewars is nothing if not complex, but that's why striving to master it forces us as players to adapt, adapt, then adapt again to what our opponents are doing. Though frustrating at times and hard to pin down, how refreshing is it to not know that "Waiqar will always recruit X,Y, and Z" so therefore "Latari will always recruit A, B, and C."
Great questions and helpful responses, all. Thank you for what you guys are contributing.