As said, yes within the limitations. There are quite a few of those though, so chances are slim that "any" session will open. With careful planning on how you do the HD session it might work. Just some of the differences.
- number of channels is less.
- sample-rates are limited
- no automatic handling of delays in plugins (may make things sound, well worse).
- processor power may not be sufficient (running everything on the main CPU as compared to the extra cards used in a HD system).
Largest problem though is the plugins. Generally a HD system lives on using high-quality plugins. Some of these are not at all available for m-powered (or LE), some are but you need to have the dongle along or paying up the money for them (which may be quite a bit). Seems like the business model of Digidesign is to make the included plugins a little bland, making serious people getting other plugins.
Well, you may be lucky.
G.