Aloe, Haworthia and Gasteria are three genera which are related closely enough to allow crossing among them. However, I have never encountered a cross between a large genotype (e.g. Aloe Ferox) and a small one (e.g. Haworthia cooperi).
By small or large I mean the size a plant can attain, at or close to its size limit. In the case of members of the Aloe family, it's about the size a single rosette/offset may attain: That's when the rosettes/offsets multiply without increasing their size.
Is pollination possible between two specimes differing greatly in size?