All files need to be exported to version 8 Illustrator eps, but these files don't support transparency, so you'll run in to problems if you use them in a design. Gradients can and are used by designers on here, but as is often the case with various software, they handle colour and gradients in different ways. In my job, quite often I've had Freehand documents that use gradients, and when I open them, Illustrator interprets them as paths to make up the colour gradients etc! You shouldn't have any issues providing you avoid transparencies, don't use spot colours, or if you do use spot colours make sure every colour is converted or expanded to CMYK colour profile and all text is convert to paths or outlines. Corel should be able to handle all this no problem, but just make sure you're bang up to date with the software to make sure.