Hello, thank you for your question.
Yes, you can reserve seats no matter what kind of ticket or pass you have.
Please note, however, that seats may be reserved only in trains which are marked «R» (reservation possible), «RE» (reservation recommended) or «RR» (reservation mandatory) under «comments» in the online timetable. You can find all information on your guide.
I wish you a lovely day and safe travels,
Chiara_S