Junglist,
It depends on where you're sending it. Some pre-press rips convert colorized tifs to CMYK instead of spot colors. Mine did until I installed a Creo xtension. Supposedly, Quark 6 addressed that issue and you didn't need an extension but I'm still having problems with it converting to CMYK. Monotone images are good but as blueark said, make sure all of the spot pms colors are named exactly the same; i.e. PANTONE 286 C in Quark and PANTONE 286 CVC in Photoshop will output 2 colors of film.