But seriously, folks...
Do what you want, obviously. I would appreciate it if there could be at least a nod towards things happening in the Warhammer World, but I suppose in non-campaign games it doesn't really matter, and we don't even have any campaigns planned yet (but it normally happens and then stalls).
All of this is just because I really like the Warhammer background, at least from the period when I used to pay attention to it, and that's what attracts me to playing fantasy games. I'm never really that interested in playing "some generic fantasy", which is what Mantica feels like to me. I'm not invested in it, and I'm too much of a miserable git to try to get into it. I also quite like the challenge of making the Warhammer stuff fit, and I don't want to let that world die. But of course, that's not your problem. Awesome as I am, I don't actually get to tell people what to do, until The Plan is enacted and I become King of Everything.
My first thought was, if you're using Basileans, could they be some Warhammer nation that's only ever been vaguely mentioned? Maybe you could make them fit for some city in Tilea or something like that. Kieron's idea is good too (although I think the gods of Law were only from WFRP? I don't know much about them. Which is ideal for a new army I guess.)
If you want to use the Elohi in some other force, I'm sure you could figure out a nice way to do that too.
Personally I'm not really a fan of the Basilean models to be honest, but that's neither here nor there.