In a perfect world, it would be better to find someone to use their spinning wheel to ply the marled yarn, as opposed to knitting with the two yarns together. The color distribution is just more uniform, more pleasing to the eye. There are spinners here @ XMTS.

If you cannot find a spinner, tho, knitting w/ the two held together should pass the "5-mph test". You know....if someone's walking passed you @ five miles/hr, they won't be able to tell the difference.

There are a lot of spinners on Ravelry. Maybe you can use that to find a spinner in your neck of the woods? or inquire at a boutique yarn shop. They might know of spinners in your area. Plying the two yarns is really the simplest, easiest thing for a spinner to do. Almost a "no-brainer", and great practice if they are new to spinning. It shouldn't take much time for them to do it, assuming they have an empty bobbin available.