no, don't use a straight needle pattern, but any pattern that calls for double point needles can be used. The same principles hold for using two circulars as for doing them via magic loop on one circular. You just have more dangling tips to contend with when you use two circulars
I agree with chickkie... Choose a pattern for mittens that is already written for working in the round and just divide your stitches in half instead of thirds to knit them on two circular needles instead of three DPNS.
A pattern written for straights will usually account for seaming (selvage stitches) and you will need to adjust the numbers for the entire pattern if knitting in the round. A better and easier idea is to use a pattern already written to be knitted seamlessly.