I would separate them if they were recently thrown together. If they have been together a few years and both do very well, it is probably not a problem to keep them together. There are some cattleyas that seem to do well grown very dry in the winter (cattleya dowiana, for instance), but most seem like more water.
I have both...and as it happens,in order to get this particular species of den. to bloom, it must have a Winter rest...usually from Thanksgiving to mid-Spring. The cattleya would not like to go without water that long. It's up to you, of course. BettyE