Totally. If you have a section of decreases, though, you may still wind up needing to knit it off onto the DPNs when you get to it... much the way most hats do.
Just remember, you cannot knit an item of a certain circumference on a circular needle that's much if any larger than that circumference. Say if your leg warmers were going to be 15" circumference, you MIGHT be able to squeeze it onto a 16" needle, but it might wind up stretching your guage funny. However, you'd be just fine knitting them on a 12" needle, because the stitches can be scrunched closer together on the needle.
In other words. A needle 2 inches bigger than the work is a no go. A needle 2 inches smaller than the work is juuuuust right.