The install manual is somewhat contradictory on the matter. In the distance table it says this:
"Magnetic measuring device other than another GMU 22 (e.g. installed flux
gates, even if unpowered) 2 feet (0.6 meter)"
But later on the same the page of the manual it say this:
"For installations with dual GMU 22 magnetometers, co-locating the two magnetometers close to each other in the tail or in one wing is recommended as this reduces the likelihood of heading splits or miscompares when operating on the ground in the vicinity of local magnetic anomalies."
Now assuming that he Dynon magnetometer can, for arguments sake, be considered to conform essentially to another GMU 22/44 for installation purposes, then the later passage would indicate it's not a problem.
Hopefully Team Garmin or Dynon will weigh in with a definitive answer.