We asked on Cunard about this. We were told (by a bar tender) that ANY sort of personal intimate contact between crew and passengers is TOTALLY forbidden. Furthermore, the only crew members permitted in your cabin are those which have a direct need to be there. ie. Your room steward or (for example) an engineer sent to repair something.
It goes further. If a crew member DOES go into a passenger's cabin without a legitimate reason, then other crew members will report this. This is because the law abiding crew members do not want to be put under suspicion if something goes missing from a cabin and a massive witch hunt goes on for 'who done it?'
A hand shake is permissable. That really is about it.
Ps. Any passenger who attempts to entice a crew member into their cabin or develop a realtionship with them should be aware of the extremely strong likelyhood of ruining that person's career prospects and causing much upset amongst the crew.