Usually, C-41 fixer for blix is not the same as B&W fix. At least not exactly. There is less of a buffering agent in B&W fix. In c-41 fix, usually Sodium Bisulfite, Ammonium sulfite, and ammonium bisulfite are the key reagents. B&W fix usually uses Ammonium thiosulfate and sodium sulfite for the key reagents.

I have used my Ilford Universal fixer in place of the fixer component in Tetenal RA-4 blix, but not for film. For E-6, the fixer is fairly close and I've mixed and matched a bit.

I wouldn't recommend it for C-41, the fixing is more critical in C-41 than in paper.