More than enough for your team's programmers.
I have not ever seen any official limit.
NI states that the FRC Licencee is to be used ONLY for FRC team member for ONLY programming the team's robot.
So each team member could activated a copy of LabVIEW. I have had teams activate up 12 with out a problem. Team school computer and students personal lab tops to work at home.
Only activate as many as your team needs. Don't abuse the generosity of National Instruments.
I'm sure there is some number NI would question the need for. Don't know if that number has ever been posted.