This was the original post (or part of it): " It occurs to me that one (by no means perfect) metric by which one can gauge the extent of music offerings at a liberal arts college is whether or not they offer a Bachelor of Music. Is there any comprehensive list out there that indicates which LAC’s offer a B.M?"
I guess I didn’t understand the premise in the first place, though I tried to 
And then this: “A conservatory is not out of the question–my son is still figuring out what he wants. But I’m actually most interested in LACs that offer a rich range of musical opportunities that do not require a conservatory-level commitment. That means that if they do have a conservatory, I’m particularly interested in those (like Lawrence, and unlike Bard and Oberlin–not sure about Gettysburg/Sunderman) that allow non-majors (or at least non-performance majors) to study with the best teachers and participate in the top ensembles if they’ve got the chops to audition their way in.”
So I am a little confused. Most of your list and many of the suggestions do, in fact have conservatories (music school is another term used but same thing in practice).
So U. of Puget Sound and U. of the Pacific both have music schools (BM) . So do U. of Redlands, Hartt and Ithaca. St. Olaf does have both a BA and BM in their music department, without a conservatory on campus. College of Wooster has a BM, BA, bachelor’s in music ed and music ed in music therapy. I am not sure the latter two would be that different in term of opportunities for BA students versus BM students, but every college is different so it needs to be checked.
Basically, for the most part, music schools and conservatories that are part of or affiliated with an LAC will offer a BM. There are a few LAC’s that do not officially have a conservatory/music school and offer a BM as well as a BA in music, but I don’t see what difference it makes.
If your son does not want conservatory-level commitment, I think his best bet might be a school that does NOT have a conservatory/music school or a BM program. I think that is the reason for the tangent. From what you have written, the most logical suggestion list might be LAC’s with strong music departments and strong BA programs in music- or strong academic majors with access to excellent teachers (on or off campus) and extracurriculars. You could also look at BA programs with some performance aspect (for instance, Harvard has performance in some musicology or theory classes; Princeton has a performance certificate etc. Your son may not be interested in these schools, but there are equivalents out there among a possible list he would like.)
There is a book entitled “Creative Colleges” that lists all schools with good music programs (as well as dance, theater, art and writing). Peterson’s also has a guide.
One way to narrow things down is for your son to choose schools based on other criteria, such as size, location and vibe and then look at the music offerings.
In sum (I tend to be wordy) : I don’t think it is true, basically, that the presence of a BM is always the measure of a great music dept. There are some great BA programs. And if your son does not want to do a BM, then the presence of a BM program may detract from his own opportunities- but not always.
I think it can be a good idea to visit schools, honestly. A list of 10 is reasonable, and applying to 6 when music is involved- but that is personal opinion. Otherwise, the possibilities really are overwhelming.