Thanks Ortron - the Knights of Blood are the ones I was mentioning. They're a bit iffy on friendliness with Inquisition, but what the heck, in this case they've all landed on a planet which is about to get wiped out, so they can't afford to be too sensitive about each other...
Incidentally, what I want to build is an illogical unit of 9 Baal Predators, which in game terms would actually not be used I guess, but would be nice as a concept - a big pile of troop-cleansing firepower. They're a bit Flesh Tearer too when it comes to going bonkers.
ortron wrote:
Yeah I like the Flesh Tearers, they love to just get caught up in the moment and kill everyone

Lamentors are also another BA successor that has some debts to pay and might need to earn some brownie points with the Inquisition but they're a bunch of emo space marines fallen on hard times....
The Blood Drinkers came across as the most level headed if your after "Red Ultramarines"
Are these the other crazies you were thinking about, the Knights of Blood:
http://wh40k.lexicanum.com/wiki/Knights_of_Blood_(Chapter)#.T2h9TsWo9fYIf none of those take your fancy, you could always say the Red Hunters or a chapter of your own creation are either a BA successor chapter OR they just favour that type of armament due to the close support roles they prefer.
With the Red Hunters for example, Imperial Armour 5 (or 6 or 7?) suggests that the Red Hunters spend most of their time supporting inquisitors in small detachments but I don't believe it mentions much more about their background and gene-seed so as L4 says "Do what works for you"