Thom,
I'm at work(last night for a few days! Finally!) looking at Photo_Screen_Saver source.... I do believe that it will run without OpenGL, and run on the WebDT!
Look at this snip from the cmd_On implementation:
string sUseAnimation = m_pEvent->GetDeviceDataFromDatabase(m_pData->m_dwPK_Device_ControlledVia, DEVICEDATA_Use_OpenGL_effects_CONST);
281 bool bUseAnimation = sUseAnimation == "1";
282
283 if(DATA_Get_Type() == "animated")
284 bUseAnimation = true;
285 else if(DATA_Get_Type() == "static")
286 bUseAnimation = false;
287 //else default -- leave default
288
289 GallerySetup* SetupInfo = new GallerySetup(w, h, bUseAnimation, DATA_Get_ZoomTime(), DATA_Get_FadeTime(), m_sFileList, bNPOTTextures, this, nMaxSize);
Basically, if the parent of Photo_Screen_Saver (the Orbiter) does not have the "Use OpenGL Effects" option checked, then the Photo_Screen_Saver will not use the OpenGL animations. Furthering this, if you create an MD using UI1, the Photo_Screen_Saver does run, just with no animations.
I may give this a try this weekend