I imagine that unless you require the front desk to not know (and good luck with that one, btw), they can't say too much if you walk outside and escort your escort into the hotel and up to your room and back out again. Even the most unfriendly hotel doesn't have a leg to stand on in that situation.
i have never had a problem with having a girl visit me in my hotel... the front desk should not hassel anyone... i tell them i have a guest visiting and to inform me when she arrives... .or i will make arrangements to meet her downstairs..at the bar or front hall... o one one guy gave me the hahahah look... i told him if he sent me a bottle of champane for free i would ask her to blow him... he sent me the bottle for free..she blew him and all was grand...