a great sound engineer / producer / mastering pofessional to just have a good ear for the music without being able to play or sing a note.
this concept sits a bit funny with me....
if you're producing a band...theyre playing a riff....and guitarist 2 is playing a riff....guitarist 2's riff has some crappy notes in it....i think its near impossible for someone with Just an ear to be able to tell that...
thats where playing becomes important...a good example is myself, i cant name chord shapes, or any stuff like that, but i play alot of tricky music, melodically and harmonically., and if there are dodgy notes in something im producing, i can sing the right one's out the artist im working with, and we move along and keep recording.
however, when u get to the mastering stage, if something's been recorded with wrong notes, or crap that shouldnt be there....there's not much the ME can do at that stage, so intimite chord knowledge really cant be that important at that stage, unless the ME recorded the project.
I think an important thing for producers and engineers to be mindful of is the language used to talk about playing an instrument....
for example, being able to tell a drummer where to ghost note, where not too....to play some triplets on their ride, or to play crotchets....
same with guitarists, be able to tell them to strum or to finger pick...
So, i think intimate knowledge of instrument performance is a mark of great producers...i cant give you names, but its something I can imagine being the case.
In short chris, my opinion on your topic is, that it might not be inconceivable, BUT, i think less BS gets put onto tape, the more mindful a producer is, less so an engineer, and even less so an ME, the more they know stuff about music theory, performance, and especially playing.
My 2c.