My venue comes with speaker systems for musicians if we want, otherwise they'll play whatever music we want. I was never dead-set on having musicians, and we, too, are having a pretty quick outdoor ceremony. Plus we have kind of a small area to
work with for the ceremony. I've personally only been to one or two weddings where they had musicians, so I never thought it was weird to have a DJ play some songs. Do what's best for you! They better be paying more attention to you and your groom
than whether you have musicians or not, anyway! =)