The key to doing them though is proper control of dominant position, or hip control. If you don't have it, they won't work very well for a submission.
I'm not sure that I understand what you mean, so please elaborate. Do you refer to the break-balance entry, where the opponent is removed from a position/posture where the hips give maximum support for movement of other parts of the body?
If so, I'd say that this is essential in any application of aikido techniques, and not just in grappling. Would you agree?
Very interesting to learn that you find frequent use for nikyo. That was my guess, which is why I mentioned it first.
Another question: Aikido end pinnings are almost always with uke belly down on the floor, and not on his or her back. Is that pointless in grappling, or next to impossible to accomplish?