Is it legal to fly Sabine TIE Fighter models with Imperial cards and bases?
Yup - standard rule is that paintjob is irrelevant.
You can have Rebel Y-wings or Z-95s with Scum paintjobs, so I can't see any reason why you couldn't have Imperial TIEs with Rebel paintjobs (though vice-versa would probably be more usual since there's no cards Imperial players really need in the Sabine pack - they'll already have plenty of VI cards.)
Edited by Ironlord