Yes, tip them what you feel it is worth. At least a couple of dollars. I know here in Atlanta my Mom tips $5+ since they take her from the curb to gate going through TSA security screening etc.
Make sure that you phone your airline ahead of time and have them record it in your record so that there is a wheel chair waiting for you.
When you arrive curbside at your departure airport, if there is no curbside check-in, have your wife notify the closest personnel and they will radio for the wheelchair to be sent for you. Otherwise the curbside skycaps can get you one.