On the contrary, I think this is a sign that the merger is on the up and up. If US Airways are indeed painting 737-200s in the new scheme after D-checks (and not in *metrojet* c/s), this seems to signify that United wants an easier integration of aircraft after the merger. Why?
Suppose that the merger goes through. No doubt, in the transition period, United will simply put "United" titles over the present US Airways planes. (This is what historically happens in merger transition periods). Now, to main a consistent look of the soon to be completely merged US Airways and accordingly new United, United would like to have as many US Airways a/c as possible look the same with United titles. If there were more red metrojet a/c flying around, the liveries would thusly be more incosistent. This is contingent, however, upon metrojet being rebranded post-merger.