I have not found a picture that clearly shows them in convoy. Part of the problem is in most convoy pictures you can only clearly identify the first vehicle or two and then the next few vehicles are really hard to differentiate.
If you look at the KtsN tables, 1,5T would mostly have been in maintenance, workshop, baggage, provisioning, machine gun, or signals units through 1941. So, you see most pictures in 1940 and 1941, but I did find a few all the way to 1944.
The 1,5T version we care about was only made for the civilian market, but large numbers were used / requisitioned to fill the Wehrmacht truck shortage.
This shortage was even worse after the winter of 41/42 where so many vehicles were abandoned due to cold, snow, and lack of fuel.
So, having a recently requisitioned civilian 1,5T Opel Blitz pressed into service as either a cargo or troop carrier (which is what the FL Blitz’s tactical symbol indicates) is very likely.
I think it’s much more unlikely to have never occurred.
Lastly, a couple of pictures I found in one book the Blitzes are all labeled as 3T but many look to very in size even though they are lined up “nut to butt,” so to speak.
