I don't think they've been nerfed, but you made me curious to see what their stats were, so I had a look on my tutu install. I don't think these creature files have been changed from vanilla...
Aerial Servant
128 HPs
AC 3
THAC0 5
1 Attack @ 23 Str
Skeleton Warrior
80 HPs
AC 2
THAC0 10
2 Attacks @ 18/51 Str
Resist cold (100), magic (90), slashing (40), piercing (50), missile (60)
Interesting! I hadn't looked at these before. Of course the skeleton warrior is badass. With his resists and AC, that 80 hps goes a long way - I'd say he's just as durable as the servant, if not moreso. The servant doesn't have the immunities that the warrior does, but he has a few things going for him: 1) plenty of hps, because resists don't cover everything; 2) nice default movement speed; 3) when that one attack lands, it counts for something. Haste adds much more to the servant's offense than it does to the warrior's, given the servant's higher damage and lower thaco.
Bottom line: I think the skeleton warrior is by far the best summons, but the servant shines in battles against fighter-types (especially golems and elementals, with their crushing weapons to which the warrior has no resistance) where there's little enemy magic.
Given the party you're considering, though, I'd say give the servant a miss. You'll have plenty of summoning power already in levels that don't have Heal in them.
