The "disable ground traffic" controls only ground vehicles specific to KMEM, not AI airplanes.
i have checked that Orbx vector hasn't messed with the elevation. and i seem to have read somewhere in the forum that FSDT airports have now been insulated against errant elevations, but alas i can't remember where. i'm lost.
The latest GSX update will recognize altitude correction .BGLs AND allows you to override the ground altitude, in case anything might have messed up with the altitude but, this would only affect GSX vehicles and jetways.
If you suspect AI airplanes might have been gone underground, possibly because some other scenery has caused an altitude conflict, there's just nothing we can do to fix it, because AI airplanes are handled by the sim, so they are affected by every possible altitude conflict you might have so, your only option is to find the offending scenery and remove it.
FSDT KMEM, of course, has the altitude correctly set to the official published airport altitude of 103.936 mt / 341.0 ft.