Yes, both Photoshop CS6 beta and the Lightroom 4 beta can be installed and used together on the same system. However, the Lightroom 4 beta expires on 3/31/2012. If you want to try the Photoshop CS6 bta and Lightroom 4 together, download the 30-day trial of the official release of Adobe Lightroom 4.
Please quit/close Lightroom 4, and any other Adobe software on your system, prior to installing the Photoshop CS6 Extended Beta:
If you encounter the dialog (below) that references the background process named 'dynamiclinkmanager' during installation, please quit Lightroom 4, and any other Adobe software on your system. Then click [Continue] to continue the installation of Adobe Photoshop CS6: