As others have pointed out, every area of music is different so there are no general rules like “you can’t do dual degree with music”. String instruments for example allow a lot more practice time with individual practice and rehearsal physically, you cannot play that much if you are a wind instrument and from what little I know of vocal music there are limits. So cello or violin allows more practice time, which would cut into time for the academic degree a lot likely (and that doesn’t count ensembles and rehearsal for that).
And herein lies the rub, and that is you may be able to get a dual degree with cello performance and engineering (despite what is often said, they generally don’t kick under performing students out of a BM degree program), but will the degree further what your goals are? And with the engineering degree, that coming from a family of engineers I know how difficult it is, if you get by in your degree but your GPA is nothing to write home about, how will that affect your ability to be in the career, when GPA especially with first jobs is huge, or these days, in getting internships that are pretty much required. I know there are kids who could do both, be brilliant on the cello and do well in engineering, but it is going to be a constant fight for time, and there is such a thing as exhaustion.
@bridgenail had an interesting point, about will a cello teacher accept someone not able to put as much time into practice as they may want them to. It goes beyond that, I can tell you that in music studios teachers can and will segregate students into those they feel can make it in music, who have the desire and ability to make it, and those who are just getting by, and they generally won’t give their best effort to the kids just getting by (and as I wrote in an earlier post, I have some insight into Jansen, and he I am pretty sure would do that). Obviously, it also raises questions about why you want to get the BM degree. If it is for the challenge of it and because you love the cello but you aren’t planning to make a career in music, a dual degree may work where as other people pointed out you can have the cello, play it as an amateur or even do some gig work.
If you are thinking it is okay, I do the dual degree, then in grad school I can concentrate on the cello and perhaps have a career, the problem is when you audition for grad school at a program likely to further your wishes, you may find it tough sledding because competition in music for admittance is tough across the board, it is even more so in the cello world, because you will likely be behind those who could dedicate the time to it.
Therein lies one of the biggest ironies of the dual degree, it seems like a great hedge, where you come out with a music performance degree but also with perhaps a ‘useful’ degree (like CS, Engineering, Accounting, etc) if music turns out to be a non starter. I say ironic because doing the dual degree is kind of working against being able to make it in music as a profession, makes it so much more difficult IMO, for the reasons I stated.
I doesn’t mean a student shouldn’t attempt a dual degree, I am just saying that it may not do what the student (or parents) want it to do, that’s all.