Hi sushi lover (I can relate),
I have been a member of the UA program for many years and like that accrued points do not expire unless there is zero activity over an 18 month period...
You will accrue miles from NH on your UA reward program, flying UA may give you extra rewards, but I'd prefer to be better served on NH ;-)
However, please don't fly UA - fly NH, after one flight you'll know what I mean - NH beat UA hands down in every way...
All miles from UA can be used across the *A network...
Happy flying.
Cheers,
AG. :-: