There's nothing against it in CASL, so as long as you meet the requirements of the CASL agreement, There's no reason why not!
Aside from the standard CASL stuff, not really. So just make sure that the customer knows explicitly what they're signing up for and what kind of messages will be sent to them and you should be good.
We don't lean one way or another, however in our own way, SimplyCast offers incentives in the form of whitepapers and guides available for free download and we find them quite effective.