my thinking on those is you will be wearing the sun lotion during the day and will need to be reapplying often. depending on what you are doing the mosquitos generally aren't that bad during the day. The other thing i think about this is slathering on deet numerous times a day is absorbing alot of deet into your body and i am not in favor of that
This may not be the most environmental appropriate thing to do but I use the mini off sportsman that has deet in it. I usually use it only in the evening so no need for it to be combo-ed with sunscreen and I just don't find low level insect repellents effective for me. A quick google seems to indicate its not a great idea as it reduces the effectiveness of the sunscreen.