A few years ago we were auditioning drummers, and went to the trouble to provide a kit for them to play (a good one, at that.) All of the drummers were fine with using our kit, except one. He insisted that he had to use his kit to "get his vibe.". We put him last on the list. Prior to his audition, we had to break down and move the existing set, then wait about 30 minutes while he set up his kit. He spent that time telling us about how much money he'd spent on that kit, and how it was everything he'd ever wanted in a kit. We were annoyed with him before he even played a lick. Needless to say, he didn't get the gig.
When bands hold auditions, they usually have to deal with a number of bassists in a few short hours. If they have gone through the trouble of providing a back line, you should use it.