Hi -- I just created an account so that I could give you a reply, after lurking these forums for the last couple years. This problem was really annoying to deal with, and I lost many hours trying to figure it out to no avail. You can't place a left margin on a <ul> for .mobi/Kindle formats. The bullets just disappear, and there's no way to get them back (so don't bother trying).
You can either use • to begin each list (list-style-type means nothing to the mobi format), and lose your hanging indent. Or, if nesting is what you're looking for, you can place your <ul>...</ul> inside of the previous <p>.
This won't be valid in epub. So if you're trying to do an epub and convert it to mobi -- the epub may get rejected until you move the <ul> outside of the <p>.
Sorry for the bad news, but hope this helps.