Sure you can. Sounds like a good idea, in fact.
It probably doesn't make much difference when you're just placing random purls (though if you pre-plan them I guess they're not so random), but knitter's graph paper is proportioned differently from the cross-stitch grid. That's because knit stitches are taller than they are wide.
You can download free knitter's graph paper from several sites:
sweaterscapes.com is one.
There are several others that give you more choices of size and style,