About hit rate

Does dex increase hit rate of mercenary and acrobat jobs?

Yes it does. But up to a minimum amount only if I'm not mistaken. If you want to land more hits using your Mercenary/Acrobat, I suggest to have Critical Chance % awake instead. Try to reach 4800% for Acrobat/Ranger/Crackshooter and 3800% for Seraph. Not sure about Mercenary. I assume it's around 3800% as well. That's the max Critical Chance cap so you'll have a higher chance to hit your target.