I've got some memory that pad's like these (usually?) can be connected to the voltage rail which the datasheet says it's connected to, but it should not be relied upon to pass much current.
That was for a completely other chip though, where the tab was connected to the positive or negative voltage rails.
It may have been for the LM3886.
Also:
L298 is an obsolete chip that just refuses to die.
Biggest problem is you loose a few Volt for the high current motor connections.
For about the same price you can get similar chips with MOS-Fets that have a low enough Rds-on to not need a significant heat sink at all, because they just pass (almost) all voltage to the motor. These usually only need a bit of connected copper on the PCB for heat dissipation.