The Defense boost from Skull Bash is only temporary, given after the, "____ lowered its head!" prompt, and after the, ""____ used Skull Bash!" prompt.
Because Power Herb would nullify the first turn of charge, there is no trigger to give the boost, so my best guess would be no. :(
EDIT: The Defense boost was only temporary from Gen I to III, then was made permanent in Gen IV. Even still, I don't think this boost would happen.