I’ve done cross IDE Netbeans RCP in the past (also in IntelliJ Idea). At the time I started, there was not very much available in Netbeans to support RCP development, so I set up my own Ant based build system. It worked out quite well, but when Netbeans IDE support catched up, I sincerly regretted not to have these new tools available!
So I would go with Mix’n’Match - change the Netbeans key shortcuts to Eclipse, use the Netbeans Wizardry to create your basic project and start Netbeans up, everytime you need to configure or change your projects’ structure (e.g. adding Modules) or branding.
I would also recommend to use Netbeans to create, modify and wire the GUI components - at least the ones that directly relate to the RCPs Windowing System - like Editors, Navigators, Explorers and TopComponents. There is some serious amount of knowledge, boilerplate code and convention in there, that greatly reduce the effort to get things done. It also prevents you from hitting some pitfalls, reinvent the wheel or introducing usage inconsistencies with the rest of the plattform.
For everything else, use Eclipse if you need to…
To share the project between Netbeans and Eclipse, I probably would try to use the Netbeans Plattform Support for Maven (Quickstart, Article), but haven’t used it til now - it may be incomplete, and the M2 plugin for Eclipse (http://www.eclipse.org/m2e/). Importing Maven projects (even hierarchical multimodule ones) usually works quite well with the current versions.