It would probably not be a good look for Mihawk, only if Aramaki forged it.
Right now this is what sets Mihawk apart not only from non df users but other swordsman. Aramaki is primarily a forest man, forging a black blade for his secondary ability would probably undermine Mihawk.
If Aramaki simply has a black blade on him like Zoro did that would not undermine Mihawk. It would only mean Aramaki is one bad ass mfer because he is likely elite af with the blade regardless, but hasn't seen the need to pull it out yet. It makes him a well rounded monster who is maxed out in all categories, with zero weak areas.