yes you can, use Traktor as normal and when you want to use RB just hit the Rekordbox button on your Nexus players to read your laptop RB library. It must be all wired in via ethernet cables for RB and USB for Traktor, and of course the RCA cables from CDJ to DJM
also there is a program called Rekordbuddy which allows you to synchronize your traktor and RB library so you can keep the files and playlists duplicated between the 2 programs. Its in the app store