In reference to the OP. Yes you definitely should have been consulted. Sounds like a lack of communication on the part of the promoter.
I play a fair few gigs with other bands on the bill, either us supporting them or the other way round. I will usually lend my gear if asked nicely and ahead of time to help the evening run quickly and smoothly. I'll give them a hand setting the amp and they are told not to change the settings once they're set.
If I don't get asked ahead of time and I didn't feel confident in lending my rig, I'd lend them a DI box so they can play through the PA. Having said that, no one has ever done anything that's made me uncomfortable.