Welcome aboard
brook! [excited]
[stuned] Good question! I'm 'assuming' yes, when you check the "scale to fit media" option, your artwork is going to be resized and I, believe,
resampled too. [confused] I'm not 100% sure 'cause I haven't conducted any tests to experiment with this, but it tends to make sense. [innocent] Otherwise, what would the purpose of the 'image dialogue' box serve? I would suggest that you try experimenting with the output results, yourself. I would, but I'm not hooked up to a printer right now!
If you use the "image dialogue box" you can change the print size by, unchecking the resampling box, and therefore, the quality of the output. IOW, an 8"x10" 72 ppi image, reduced to 4"x5" will increase your quality to 144 ppi...in most cases, suitable for print.
If anyone else with some real experience or knowledge in this area, knows otherwise, you'll soon hear from them.