Different variants within a species are definitely crossable (for instance, I just recently purchased an A. barteri var. glabra x caladiifolia). Cross-pollinating distinct species is more of a trial-and-error thing, though... naturally, the more closely related the two species, the more likely hybridization is possible.
So, in short, which two Anubias are you trying to cross?
Just had 2 anubias species flowering at the same time. I don't know how to pollinate them but they both were dropping pollen so I rubbed them together. Anubias nana and Anubias 'Gasser' Would be cool if they were able to cross.
pollinating anubias 
Linear Mode
