Looking at that photo WTD the 'tender tended not to be as effective if propelled ahead of the diesel and also caused problems when stopping at a signal. As it could lead to a "SPAD" [Signal Passed At Danger]. So whilst yes they were propelled if the tender was between the loco and train the added wieght of the train helped with the braking. I've a metal kit of one I've yet to get round to assembling.
The photo also looks like it may have been taken at Pelaw on the line from Newcastle to Sunderland. There was a 3 way junction behind the photographer. The branch to the left went to South Shields and had a third rail for the Tyneside electrics, the line straight ahead went to Sunderland and Teesside, the remaining line that swung off to the right went through Washington and was part of the "Old" East Coast Mainline and connected to the current mainline at Tursdale South of Durham, just North of Ferryhill.