there are too many differences imo. anderson is holding his left blade overhand instead of underhand. alucard is holding his gun with his right hand, not his left. highly doubtful that any resemblance was intentional.
^Holding your swords horizontally like scissors around your opponent's neck, and pointing your gun at the bottom part of your enemy's jaw. Maybe is not a direct parody or reference, just a coincidence. Over analyzing, katanas are longer than bayonets, and I doubt our heroines are more than 6 feet tall, like Alucard and Anderson, therefore they changed their poses slightly.
Its a coicidence. Now show me a frame by frame mirror image of said battle and i'll say parody since Panty and Stocking is supposed to be a parody show.