It terms of how you’re sampling the rotation it appears correct. I’m not sure what the fabrik rotation does (haven’t used it myself yet), if you’re having trouble using it, you could instead simply rotate the characters hand bone using FK (transform bone) *after *you do the hand IK.
Do note that you will likely have to rotate your leap rotations such that they are in the bone space. For the hydra, I adjusted to the local space using something like
There should be more details on this in the hydra thread. You can change axis directions or swap them around using break rot, but all rotation transforms should be combined using combine rotators, which uses quaternions in its implementation, this ensures you do not have a gimbal lock by converting axis.