I applied to LLU this year and was accepted. (I'm not going though, mostly b/c I also got into public schools, and just am not interested in extra debt.)
Anyway, yes, there is a chapel requirement (as in, you have to go once a week), and they are very serious about the lifestyle stuff (no drinking and smoking)--I'm Episcopalian, and I was very plain about that fact on my application--and before granting my admission, they called me to make sure I could handle the no-drinking bit. (I said I drank moderately and responsibly on the app.--plus, I take wine with the Eucharist each Sunday.) They are also very serious about the Sabbath, which they keep from sundown on Friday to sundown on Saturday. Apparently, most businesses in the town close (although this would really be no inconvinience, you are in LA, afterall) and the library closes--pretty much everything but the hospital. A lot of adventists also follow a fairly strict diet--the hospital cafeteria is vegetarian (not vegan, though), which I thought was pretty sweet. I think they do offer meat choices to patients. Basically, the bottom line, from my experiences with the school (admittedly limited--please, LLU students: chime in!) is that if you're SDA, it'd be a terrific place for you. If you're otherwise protestant, and are willing to change a few of your denominational patterns, or at least respect those of the adventist church, you'll be happy there. If you're not a person who considers Jesus to be central to your religious life (or if you don't particularly have or want a religious life), you might be happier going to a different medical school.