Alright ... Let's say you had a very pretty woman (on the outside), who was very ugly on the inside (bad qualities, rude, no morals/values, etc.)that ugliness will start to seep out and, although she may be beautiful on the outside, you'll feel very disgusted to even look at her because she's so ugly on the inside.
Now, take a woman who's not that attractive on the outside but is so beautiful on the inside that she makes you want to be a better person. That beauty will seep (the same as the ugliness) to the outside and you won't see the unattractiveness that you first saw.
I believe that inner beauty is more important than outer beauty. But, it's just my opinion. A lot of people want or need to have their mate look great on the outside. I've been asked on several occassions, "what were you thinking?" with some of my past boyfriends because they were so unattractive ... And my answer is always the same. They had a great personality, they were fun to hang around ... I wasn't looking for the way they looked on the outside. I was looking for the way they looked on the inside. How they made me feel and how they treated me. (even though every single one turned out to be a jerk later on in the relationship, lol.)
so, to answer your question ... No, I don't think your mate has to look good on the outside in order for you guys to have a wonderful marriage. It's how you guys make each other feel when you're around each other. Beauty on the inside out-weighs beauty on the outside in my book. Good luck! :-)