Missionary work actually might (and I mean might) fly with certain schools. I know PBAU in south florida is a baptist school, so maybe they might be sympathetic. but...
This is probably one of those questions best answered by you contacting the university in question. I really dont know how anyone here would be familiar enough with the deferral policy of X university to provide you with any useful guidance.
If you are looking for opinions though, I would have to agree with the earlier posters and say no. I have read posts where people have deferred over medical reasons and b/c of inablility to obtain funding for a university not yet accredited. Then again, I dont think I have seen any posts referring to missionary work either... so go fig
~above~