What is traditionally the side dish you eat with saltimbocca a la romana?
I would venture to say there is no one specific traditional side dish. If you go to Italy you aren't going to see saltimbocca with a side of anything on the menu. You can pick you primi and contorni yourself. I think s very simple mixture of roasted or grilled asparagus and/or squash would be very nice.
If your wanting traditional and you are making a roman style saltimbooca (saltimbocca alla romana) You can try to pick a primi and contorni that would be common and traditional to that region. For example you can do "bucatini all'amatriciana" as a primi. With a nice fennel and orange and/or artichoke salad as a side And of course to the season it is being prepared. To me that is really what is "traditional" Italian cooking.