I think the allegiance has legs, but its very specific.
Untamed Beasts with the charge bonuses will tie things up very quickly and be a good chunk of wounds for your opponenet to chew through while your hammer units get into position. Probably some nice combo with Belakor to stop those harrassed by the beasts from doing anything. Alternatively, battleline Iron Golems to sit on objectives is cheap as chips and useful. Maybe there is room for Splintered Fang with their mortals too. But like people say, these guys not having marks means they cannot be buffed by prayers so? Who knows.
S2D are all about buffs and making the Warshrines leaders and having two prayers that go off on a 2+ is rather tasty. They can do extra objective stuff in a lot of battle plans while providing very reliable boosts to friendly units. You could focus on undivided and hand out re-rolls to hit, wound and charges to two units - while making anything nearby get a 6+ DPR and immunity to battleshock - I think there is definately something in that!
Gresh could also feed into this giving +1 to hit too for a CP.
Like all S2D stuff, its not outwardly powerful, but there is a lot of moving parts and buffs to take into consideration.
No artefacts is a total oversight though I feel... but going chamon and ignoring rend -1 on your warlord warshrine is a decent option!