That restriction is applicable only when the pantos on each of the MUed locos are raised and those locos are connected using UIC cables. Normal MU operation.
In case of MUed WAP5, only one panto supplies power to both locos. Both locos are joined together with a High Voltage (HV) cable. UIC cables only carry low voltage control signals. HV cable will carry 25 kV AC for powering the slave locomotive and thus avoid the need of having the slave locomotive use a pantograph. This is important for high speeds where multiple pantographs will introduce heavy turbulence in the catenary, leading to failures. Hence, they won't be restricted :D