Ask first, photograph 2nd. The old saying that it is easier to get forgiveness than permission is a good way to find yourself in a lot of hot water from which you may not be able to extricate yourself. Several posts mention that taking photographs on the ramp is considered as a suspicious activity. If the FBO or somebody seeing you notifies the cops or airport security you might be in for an unpleasant experience. So why take a chance? Ask first!
Don't forget your motives DO NOT MATTER! The only thing that matters is how the other person reacts. It is like hugging a coworker who just shared a personal tragedy. If they misconstrue your actions HR is probably going to have a counseling session with you. Even worse is when you and your co-worker are ok with it but someone else sees it and reports you to HR. Bottom line, you are still the one with a problem and black mark on your record.
Why give the press and stupid bureaucrats an opportunity to tarnish GA?
Wag more, bark less, and never bite first