Yes, no, and maybe. But I consider it an exploit.
It breaks down like this: Jump Gate Construction Ships may not move while building a jump gate, but a ship with a jump engine, parked on a jump point, that is used to 'ferry' a task group across the JP, doesn't actually move as far as the computer is concerned.
So if you consider the ship to be using its jump engine to open a temporary path across the jump point for other vessels to travel through, then sure, no problem.
If you, like I, consider the ship mounting the jump engine to exert some sort of field that 'picks up' the other ships - two or however many at a time - and carries them across to the other side of the JP, then no. It requires the jumpship to move, and jumpgate construction requires the ship not to move.