Not tried that one C&B...
I'd use three game logics, (the markers) three triggers and one tank...
Oh and the following in the init.sqs :
randtank = random 3
Place the three game logics where you want 'em, then create three triggers with the following in the condition and OnAct fields...
Trigger1
Cond: randtank >= 0 and randtank < 1;
OnAct: tank setpos (getpos name of first game logic)
Trigger2
Cond: randtank >= 1 and randtank < 2;
OnAct: tank setpos (getPos name of second game logic)
Trigger3
Cond: randtank >= 2 and randtank <= 3;
OnAct: tank setpos (getPos name of third game logic)
Might seem overkill, but it works like a charm...
Will try out your suggestion C&B