I'm really struggling with this too, not trying to be a naysayer.
Just seems like Ulm demands high scales because of the resource demand of their troops, and the necessity that creates for additional castles (not to mention the castles needed to get any kind of decent research). At the same time, they suffer from a horrendous lack of magical diversity, so need some serious help there, and can't have an Imprisoned pretender, because they need the help soon. The scales need is so great though, that to me it's unthinkable to be Awake, meaning that without that first year, your pretender is going to be crunched for time.
So, I agree that Blood Stones are amazing, and are immensely valuable for Ulm. But what I'm wondering is if it's worth it to worry about on your pretender, just to pop out and Blood Hunt for 5-6 turns to empower 1 guy.
And still, you find yourself torn between Staves of Elemental Mastery, Blood Stones, Clams, Fever Fetishes, Robes of the Magi, Flaming Skulls..... It just seems like while these are all obvious options for how to potentially bolster Ulm for the late game, that it's an awful lot to ask for all at once. I mean, you don't often get that much done even with nations who can do -some- of it with national mages.
Especially when to accomplish it, you need so many paths, and so many gems, that you'll have to manually site search for years to get what you want.
I think I'll start a game with an A/E/S pathed pretender, and experiment with the B0 hunters, see if I can get enough slaves to make something interesting happen.