My experience has been that if you are honest about what you are doing there is no problem at all. Two examples-

My best friend got married a couple of years ago, we used my AA miles to fly her and her husband to Maui where they stayed with friends. (They were very cash poor at the time due to starting their own business, etc) We also booked them one night at the Wailea using my husband's points and his Marriott cc. to hold the room. Called the hotel and explained. The hotel treated them awesome, room upgrade, plat arrival gift etc.

We had booked a family trip in San Diego but my husband's travel plans changed so that instead of driving down with us he had to stay longer on a business trip and flew in to SD to meet us instead of returning home to LA. When I arrived with the kids I explained to the hotel clerk that my husband would not be arriving for a couple of days, she left the room on his card, gave me the plat arrival gift, lounge access and 2 keys. No hassle.