Yes, in some cases. They were more likely to succeed in an appeal to repeal civil action taken against them (though it was still difficult). There are many cases regardless of this, however, where ex-Imperial Army Jews were still treated as any other Jew. The most benefit that could be afforded being a veteran was if you were married to a German woman and were a German citizen yourself, in which case the rules could be much more lenient on you (but still massively dangerous).

Within Germany existed mandatory state homes for Jewish families and in many of these homes were families with Veteran Jewish men married to German woman. Any small infraction found during a raid or reported to the Gestapo in these homes was grounds to be arrested, but the rules were more lenient on veterans. However, they were not treated well in these homes, and they would often be crime ridden as Jewish families would have to steal to stave off hunger.

Treatment in imprisonment could however be slightly better for veterans, depending on the imprisonment. Victor Klemperer was incarcerated for a fortnight in a police cell and was treated relatively well. However, in the rapidly filling prisons and concentration/death camps, little favour would be afforded to veteran Jews.

Freidrich Solmitz, another Jewish veteran married to a non-Jewish German woman, had a better time of it, as they had raised a Christian daughter together. They got to live in their own home. Even still they faced a strenuous existence, and by 1943 his wife Luise weighed just 96lb from massive reductions in rations for any Jews or Jewish families.

Was treatment really better there? No summary executions?

Probably wrong, and added to make the film seem not massively hopeless. Summary execution, working 'til death, and death via negligence/disease were common across most concentration/forced labour camps (though the SS tried to stop outbreaks of disease in camps and avoid killing too many, because in the end the camps were primarily a tool for manufacturing - the V2 program was massively intensive in effort, and it was almost entirely completed via slave labour utilised across various camps. The SS of course tried to stop disease mostly by killing and safely removing any infected individuals, so not quite good lads by any means still).

Would they have been spared and sent to Theresienstadt with him?

It's possible, but it also depends on logistics. Is a train coming through at that moment and not for quite a while longer? It's possible they would have been sent with him simply because they were there and so was the train to the camp. If no train was nearby and there was a ghetto they would be left there and later rounded up, possibly as one group, to the incoming train. The Nazis didn't care an awful lot about that sort of thing anyway considering how many died on the way to the camps on the trains. Every carriage after every journey to a camp was chock-a-block with dead that were pulled out.

Despite what jokes and stereotypes would have you believe, the trains weren't run efficiently all the time, or even a lot of the time in Nazi Germany. Lots of problems with schedules, lots of layovers, fixing railway lines in the East after partisan activity, and just general neglect. These were a considerable factor in many otherwise avoidable deaths on the train carriages.

Sources:

Richard J. Evans, The Third Reich At War

1973 BBC Documentary, The World At War: Episode 20 - Genocide