Main question:

If you look at the basic structures fcc and hcp, you find that e.g. fcc(111) and hcp(001) are both maximum density packed surface structures with triangles. Therefore these two facets match with each other and you can do epitaxy there. Please be aware that, since fcc has an abcabc stacking and hcp just ababab, an fcc-derived layer provides one additional "structure variable" about the stacking direction, so you can expect epitaxial growth without any texture issues of hcp(001) on fcc(111), but if you try it the other way round, you can expect the fcc layer to stack both abcabc and cbacba (symmetry-equivalent to a 60° or 180° rotated domain), so if you check the texture with an XRD pole figure, you can expect twice as many spots as on a single crystal.

Secondary question:

The adatoms can be bound to the substrate by any known kind of bond, be it van der Waals, covalent, ionic, metallic or quite often a mix of them. That's not a question of the crystal structure but more a question of what the specifice atoms prefer when they react with each other.

Cubic substrate 111 plane is equivalent the hexagonal 0002 or parallel planes equivalent. So, it is not a problem.