Jaws of the Beast does not take into account on-hit effects for healing, unless the on-hit effects themselves apply healing. For example, if you have Wit's End you wouldn't heal more from Jaws of the Beast if you're above 50% health, but you would heal more below 50% because Wit's End heals you as well.
I've messed with it in practice tool, looks like you're right. Jaws of the Beast definitely doesn't heal for on-hit effects (botrk deals 600-ish damage to the dummy yet WW only heals for like 200), but Infinite Duress heals for all the damage he deals while channeling, which includes all on-hit effects (I could heal from 0 to full with it).
Warwick builds
I've heard he supposedly heals off