I think with the grades you're talking about, you'll be a strong candidate, regardless of undergrad institution.
The first swipe the admissions officers take is probably purely based on LSAC numbers. If the LSAC accepts your GPA, you're fine. (And they accept any regionally accredited college gpa.)
The reality is that comparing one college undergrad GPA to another is pretty much like comparing apples to porno movies. There is absolutely nothing that, say, a degree in biochemical engineering from Harvard has in common with a degree in communications from a tiny liberal arts school somewhere. Nothing. At. All. To compare a 3.5 from one to a 3.5 from the other is just idiocy. They might as well be comparing hair length and eye color.
However, one of the decision criteria is undergrad GPA. if you've got one, that's what they'll use. If it's a good one, good for you. Although I could see you being at a disadvantage when it comes to, say, admission to Yale, that's only if you are up against an equally qualified candidate from an obviously superior undergrad education.
However, the more prestigious the school, the more likely they are to look at the intangibles you mentioned. So, it's quite possible that an admissions officer would say, "Well, it's a 3.8 from UMUC, and this other guy has a 3.8 from Wisconsin-Madison, but frankly, the guy from UMUC has a lot more impressive extracurriculars, including keeping our nation safe."
My opinion is that once you get away from, say, the top 3, the UMUC thing won't be that much of a disadvantage if it is one at all. And even within the top 3, they take a lot bigger look at the whole candidate than most other schools do.
The key for you is to nail a monster gpa, which you are already doing. Then, to nail down a comparably monster LSAT. Apply with a 170+ LSAT and a 3.8 from UMUC and you're going to have more than one T14 acceptance to chose from.
That's my decidedly non-expert opinion, but I think you're going to be in great shape.