Haven't tried those pickups, but I have a Duncan Screamin' Demon in the bridge (it's splits into a nearly convincing single coil sound) and a Stag Mag in the neck...lots of great and useful tons outta this setup. THe Stag Mag splits fantastically as well, it's sorta designed for that. Anywho....
How much gain/overdrive are you using? Dimarzios are wax potted, and I haven't really heard of their modern pickups without covers going microphonic. With enough gain you can get just about anything to feed back.
In the Morse I'd go with something a little more vintage-y. Maybe an Abraxis or a Mule. If you want something a bit hotter the Cold Sweats have a really cool kind of 90's metal vibe with nice tone and split really well.
Definitely had a Dimazio go microphonic on me. It was on an Ibanez Petrucci JPM90HAM. The Tone Zone in the bridge started squealing like a demon one day. Nothing changed in my rig/settings/volume/etc., it just went microphonic. Took me a while to figure out what the problem was. Needed to be dipped in wax again.