IMO this depends, is the fuman chu on frozen?
If this lion is not on frozen foods I would say no, because they can be shy and can be tough to get on frozen foods. A 125g with a Fu man Chu will not be so easy to train, or keep this lion in a smaller tank until it is trained.
If Yes, I say go for it. have lots of rock and cave to allow them to establish territories, I would place them in the tank on opposite sides and keep an eye on them. Though the Fu man chu can be shy it can be aggressive towards the same species, the fuzzy has been known to harass other dwarfs. I have kept my fuzzy with other dwarf species and no problems, this is just something to keep an eye on, and be prepared to separate if it does happen.
Kaye