[thejeff]

Frankly, B1 casters really aren't much use in combat. Since they have to use slaves to cast, they really only get one maybe 2 spells. Of what you're likely to get Imps probably are the best. If the thug is relying on buffing, the imps might even get him.
Trying to get them close enough to cast other blood attack spells doesn't work reliably and just leaves them without time to run away when the PD breaks.

If you really want to defend them, give them more defenders. Archers help alot against he cheaper remote attacks, if your PD doesn't have any. Thugs generally require other thugs/elite troops or real mages.