Avid today stated that they plan to support 10.8 and the Gatekeeper feature, and that they are working on code-signed versions for 10.8.
They also advise anyone wanting to test out current versions with 10.8 to bypass Gatekeeper:
1. Hold down the Control key
2. Click on the installer package of the installer you wish to open. A menu will appear near the cursor
3. Select “Open” from the menu that appears. A new dialog box will appear
4. Select “Open anyway” from the dialog box. This will allow you to proceed with installation regardless of Gatekeeper settings.
You can also choose Gatekeeper settings in the System Preferences window to suppress these warning messages, but you should be aware that lowering the security level such that unsigned applications can be installed without signature checking increases the risk of inadvertently installing and running software that may harm the system or compromise the safety of your data.