Gail, if your husband was in combat in Viet Nam then he most most certainly can join the V.F.W. !!! He should have received a Viet Nam Service Medal for combat service.
Here is the link for all those eligible veterans who have received a combat action ribbon for service overseas, who can join the V.F.W.
Viet Nam Service Medal
July 4, 1965 until March 8, 1973
http://www.vfw.org/pdf/eligibility.pdf
No he's a Vietnam era Vet, did his hitch in the USAF, A & E for the Mace Missile system. First on Santa Rosa Island, FL, then Okinawa. Which only makes him qualified for the AM Legion.