Hi Scotty McP and welcome
I'm not a promoter but know a few involved in DJing and I think it's the owner of the venue that has to make sure the insurance is in place because in a litigation sense it's the owner who is taken to court and not the promoter. The promoter can be considered more as an employee so it's not their responsibility to make sure public liability is in place and a venue owner who doesn't agree and tries to make a contract that passes the costs and liability on to a third party would be well dodgy. It might be fair for a venue to charge a nominal fee to promoters that is used towards insurance but that would have to be clearly stated in the contract and still wouldn't make the promoter liable in any court action over damage/injury. Regardless of the event it's the owners who need to make sure people arn't going to trip on the badly lit stairs and lose some teeth. Being sued for exposure to bad jokes would be an interesting test case.
I could be wrong on all the above so if I am sorry about that It's good to get advice from tinternet but if you're taking it seriously then you should get advice from specialist solicitors and some even give a free hour initial consultation so just make a note of all the questions and then squeeze them all in to the free hour. I think the biggest single best advice out there is read the contract carefully and be prepared to object to anything you don't agree to.