Actually using detect thoughts on raphael is pretty safe, even though it might seem risky at first. The spell works during conversations with him and while he definitely notices your mental probing, he mostly responds with theatrical mockery rather than any real hostility. If you're successful with the intelligence check, you'll get some interesting insights into his true nature, especially about his plans and how he views his allies like korrilla.

The most interesting part is how he references your attempt to read his mind later at the house of hope, with a bit of playful taunting, but nothing that actually hurts your chances. His surface thoughts come through as cryptic rhymes which, while not super clear, can give you useful hints about his schemes and the contract negotiations. Tip - pay attention to what he thinks about other characters since that information becomes pretty valuable when dealing with haarlep and korrilla in act 3.

Be ready for some resistance though since he's an archdevil's son after all, but the rewards of understanding his true motives usually outweigh any minor awkwardness in the conversation. Just remember that while he might play along with your mental spelunking, he's definitely keeping track of your actions for future reference.