Offhand, I'd suspect you're wasting your time calling Universal - they aren't going to do ANYTHING unless DP violates the contract (it's a contract - that's sort of it's purpose). It's not like they can whip the license out from under DP if they wake up pissed off one morning. They have to follow the contract, same as DP does.

Call them if you like, but unless you can show them something that makes them think DP is violating the contract, they aren't going to do anything. And honestly, even if DP IS somehow violating the license, they STILL might not do anything, because it may not be worth their time - it's not like leaving the contract in place is costing them anything (who else would they sell a BL pinball license to?).

That said, it's certainly not going to cost anything but your time to call Universal. I would advise that you have specific things that you want them to do when you call - if you get hold of someone sympathetic and you simply whine about DP, they aren't going to care. If you say 'please do <specific thing> to help us', then if they are feeling generous with their time, perhaps they'll do X. And by specific I don't mean 'please apply pressure'. I mean 'Please call <this guy> and let him know you're getting annoyed buyer phone calls'. Specific requests might generate something, generalized rants will NOT.

Given the laser focus on money that Universal has, do you really think that they'd even spend lawyer time talking to an unknown like DP if there wasn't going to be cash up front? Again, never say never, but I'd be VERY surprised if someone authorized a license deal that didn't include an up-front payment. Not to say that there isn't more per machine, but you bet your money they aren't depending on the machines to sell to make something out of this deal.