I am looking for a smaller school in the northeast but I still want to be a part of marching band, since the schools are right next each other if I become a student at Amherst can I participate in the UMass band?
I would say find a smaller school in the northeast that has a marching band. If you want to join the band at UMass, then go to UMass. Can’t have your cake and eat it too—make a choice.
Don’t mean to sound snarky, but my taxes support UMass and its outstanding marching band.FOR UMASS STUDENTS.
No you can’t play in the UMass Marching Band if you are a college student elsewhere.
Is marching band a course? Students can cross register for courses so you might be able to, although it may take more time to get to practice than you think.
Agree that OP could be referring to both Amherst and UMass Amherst being in the same consortium. But it’s a question for the colleges. (Students in the NE consortium UM Lowell is part of can enroll in their band.)
Many LACs have pep bands rather than marching bands. If you want to go to Amherst you should see if that is an option.
@MADad I suspect he was asking because of the unique consortium between Amherst, UMass, Smith, Mount Holyoke and Hampshire. UMass students are allowed to take a few classes at Amherst College if they like and vice versa. He was wondering if that consortium extended to extracurricular activities like marching band. As a general rule, it does allow for that, but I don’t know if marching band is included.
https://www.fivecolleges.edu/students/clubs
I was a reasonable question, actually - not an effort to steal your tax dollars. 
D went to Mt. Holyoke and enrolled in a club at Hampshire that MHC didn’t have. All was well until it was discovered that she was not a Hampshire student–she was asked to leave and not come back–the club was for Hampshire students.
So I would say the Five Colleges Consortium doesn’t extend to clubs and activities.
Here ya go, @c0llege143
https://www.fivecolleges.edu/music/ensembles
“The ensembles and orchestras listed below are open to all Five College students by permission of the director.” It includes the Minuteman Marching Band.
So for further info, OP talks to the school or the director.