My Dentist Suggested Drilling an Opening in my PFM Crown in Order to Relieve Pressure. Is This Okay?

It sounds as though you  have an abscess associated with  a tooth and that your dentist is wanting to relieve the pressure with that tooth.  This will allow the infection to release, hopefully relieving any pain that can may be occurring.  A root canal could then be performed. This should be the only reason to place a hole in your crown.  Good luck. 

Hi Vannek  Your dentist would want to drill a hole in the crown to release pressure built up and give you relief from pain. If your doctor said the tooth was infected or the nerve inflammed, then this procedure will help you until you can see an endodontist for a root canal. It is only a temporary solution to make you more comfortable. If you do not have pain and he never mentioned infection or root canal than there would be a reason to get a second opinion before you allowed him to do it! 

If you have an abscess or inflammed nerve, your dentist may want to create an opening in the crown to relieve pressure so that it can give you temporary comfort and reduce any throbbing pain you may be having. But is that the case? Are you feeling any pain or throbbing on the tooth with the crown? If you're not having any pain, then I'm not sure why the crown is being opened.

Sounds like you might have a nerve abscess which will require Root Canal. Any mention of that? If not, i can't imagine what he is trying to accomplish by drilling a hole.
 

Only if the proposed opening is to perform a root canal.  Otherwise its not ok.......................