Its not possible to browse photos on an external device like a DSLR camera, you would need to copy the photos manually to the tablets own storage to a folder that PS Touch would recognize (like the Pictures folder) using software from the tablet manufactuer or some other type of File Browsing application.
Is it something that may be possible in the future? Is this something that
carousel can do, and if so, will that be made available on honeycomb soon?
You could create a new Idea thread as a feature request for PS Touch to have this functionality in future releases.
Whether you would be able to do this kind of workflow in Adobe Carousel would depend on how the camera communicates with the device/system. Note: Adobe Carousel is only available for Mac and iOS devices currently. If your camera mounted as a volume you could potentially do this kind of workflow on the Mac desktop version of Adobe Carousel to import photos from the camera. You could test it out with the 30 day trial Adobe Carousel.