IMO, intergrating the two runtimes will lead to disaster.  File components essential for current version Poser integrity may get overwritten.  If there is no urgent reason to delete PoserPro, simply use it's runtime as an external link.  External runtimes help in organizing content as well as keeping the workload overhead down when running your application.  I have both Poser 7 and PoserPro runtimes feeding Poser 8 without any problems.