From my experience and before I signed up for smart gates, I was always able to access the Fast Track line, with or without a Fast Track card. These cards are usually handed out on the plane shortly before landing. The person monitoring the line always waved me through.
Your friend should have no problem joining you in the Fast Track line. If the cards are handed out on board, you could always ask for another one.
It can happen that the Fast Track line is longer than the other lines so a person in the Fast Track line could be delayed.
Personally, I wouldn't bother with the Marhaba arrivals service.