No they are free to move as they like in the movement phase; and since they cannot disembark outside of the movement phase they are not effected by Glory hogs in the assault phase(but assuming they can shoot, they must shoot at the tank)
FAQ supporting text:
Q. Can a unit of Tankbustas that start a turn
within line of sight and/or charge range of a
vehicle, move out of line of sight and/or assault
range in the Movement phase in order to avoid
firing or charging the vehicle?
A. Tankbustas are free to move as they please in
the Movement phase. They are only bound by the
‘Glory Hog’ rule when shooting and during the
Assault phase.