[iDarkCara]

Source: Zombie Hand

If you get grabbed by zombie hand and thus rendered immobilized while having summoner as an active class (And skills normally required to ingrain), you are treated as if you're ingrained and still gain hp regardless of what inflicts immobilize.

I have yet to check any other source of immobilize, but I assume this is the case.

I'm not sure if this is intended but I suspect it not to be,

Synthesis just reads: At the start of a new round, if the owner of this skill is immobilized, all enemies within 3....