Hand-rotating a 300SD engine?

I don't have much experience with diesel engines. The starter on my 85 300SD is locked up. The wife says it wasn't running abnormal or hot when when shut it down, but when she tried to start it a short time later, the engine would not turn over. I checked it, the battery is still up....and yea, the starter is engaging but is not turning and so it is drawing a huge current that heats the starter wiring up very hot. So first thing I have to remove the starter. I can connect it up to my jump-starter to see if it runs out of the car. (but I guess this is not a very defintive check as there is no load on it when not installed). and I would like to be able to see if the engine is itself is locked up/seized.....but I am thinking that on a diesel, you can't turn over the engine by hand. Is that right...in that case how can you determine whether it is seized or not. I am pretty sure the engine must be okay, since there was not a problem before she shut it down. But still I would like to confirm a bad starter by knowing for sure engine is not seized.