You have to know the rules for the pallet, and the rose show schedule will tell you what is allowed. If they allow large-flowering climbers (LCl) or shrubs (S) in the class, then it would be fine. If not, then you cannot enter these roses into the pallet class. Each show is different, so you have to have the show schedule for that specific show.

The pallets have a small flower tube underneath each opening which holds water.

How old is your DD? I have pretty long stems on mine, enough to exhibit in the regular Shrub class.

you might try picture frame also if you have only short stems. I think I may try a picture frame entry at the next show I enter. Sometimes I have beautiful blooms but the stems don't seem long enough.