Yes he can just use your card. All of my family members used the gym at one time or another (except my 9 y/o) using either my or my sons card. I believe that card is good for your whole party. At least we didn't have any problems.
I registered for Loews membership about two months ago and never received a card. I called, and they gave me a number and said they were sending the card. Then, I received some mail regarding their new program, and my number was listed on the literature. But I never got the card.
I hoping to get some of those perks, but it looks like I have 2 strikes against me: entertainment rate and NO card! :