Is this mod compatible with NHF?
To be honest, I have no idea. I haven't downloaded NHF yet, and I haven't even had time to properly play the regular Heroes 5. But as far as I understand, it changes a lot, including the characteristics of the standard heroes from the tavern. In short, there will probably be a small conflict between the mods.
And if in detail:
1) First, NFH will load and create a list of heroes. There are 3 options here, depending on which heroes from the tavern will be:
1.a) absent
1.b) modified
1.c) new heroes added
2) Then, xReplayser will load.
2.a) absent heroes will remain absent
2.b) modified standard heroes will return to their initial characteristics from the vanilla version and new models from xReplayser
2.c) new heroes will remain unchanged from NHF
Conclusion: so in principle, you can play and not worry, the mods should not conflict too much, there will be no critical errors that drastically affect the gameplay.