"Now my question for you is, does having a casino line of credit help get better comps?"

Not unless you use it. It's all about play.

Say you open a $10,000 credit line.
Say you draw $5,000 and show only a few $100 in play. Do that a couple times and they more than likely will cancel your line.
Casinos do not want to be a bank account. A credit line is for playing at the casino that gives you the credit line.