From my experience - get it out there.
I can't personally stand looking at my dealers websites with no images of vehicles, it drives me crazy. And I have been back and forth with this - not feeding vehicles until there was a photo to sending as soon as they hit the DMS.
Sending without photos muddys up the reports a little and isn't as eye appealing (to me) but too often I see leads, I hear call and I wittiness people coming in on a vehicle that has little data and no photos.
Note: 2001 Audi Quattro Wagon - no photos = phone calls (no matter the price)
2009 Honda Civic - no photos - no likely
Point is - depends on the market supply to demand.
Something you could test, I thought about doing this but not sure if there would be a reason to it other than my own personal reasons... exclude vehicles with no photo from your dealer website but allow these vehicles to feed to the listing sites.
OR take advantage of the No Photo slot and have something like the following.
"Photos coming soon - Call XXXX or email XXXX to expedite vehicle photos"