The vet visit went exceptionally well. It was a new vet and she was amazing, extremely thorough exam and very communicative. She checked him "head to tail" and the only thing she noticed is that he felt pretty gassy. Other than that, no bruising or swelling in the mouth that would indicate complication from the dental, heart sounded great, lungs sounded great, bladder and colon felt normal. She even checked his back muscles to see if he had any arthritis issues, which he didn't. Overall she said he looks exceptionally well for a diabetic cat this old. They also did in-house blood work and everything looked normal, the elevated WBC and infection markers from the labs we did last week were gone, so looks like the dental did the trick.
So she wound up prescribing Metoclopramide, which said is an anti-nausea but also is supposed to help the GI track get into a normal rhythm. She said sometimes the anesthesia can disrupt that and with the gassiness she thinks his GI track might just be stopped and that's why he's not getting the digestion in to keep the ketones out. So we start giving him that along with the cerenia for the next couple days until things even out hopefully. I'm also going to try and pump a little more food into him. I realized I was syringe feeding him his "normal" amount, which is 1 5.5oz can per cycle, but lately he's been eating almost twice that calorie-wise, so that could also explain it.
Unfortunately the vet was just a fill-in, I guess she just moved down from Pennsylvania and they're not sure if it's going to be a full-time thing or not. Either way, I'm going to find out whatever practice she does go to and start going there so she can be his full time vet.