It's fine. If your printer can't handle fireworks files.. you can always save out a high-res JPG for them.
If you plan to use mamemarquees.com... they like RGB files. Fireworks is primarily a web graphics creation software... if it doesn't have multiple color spaces to choose from, then that means it is defaulting to RGB. Just remember to make your file at a minimum of 150 DPI, better if it's 300 or over... but 150 at a minimum.