I’m not sure if David has seen your question yet, but the answer is generally yes, both types of gametes may be produced by fertile triploid roses. However, for a specific cultivar, the ratio might vary and would be difficult to know except through direct observation. Trial and error can at least give you some idea whether a rose might be usefully fertile in a particular direction. With 'New Dawn’s long breeding record, it seems that it might either favor the production of 2n gametes or else breeders were primarily interested in crossing it with tetraploids–which is probably true regardless. The good news is that its fertile pollen should work well with most fertile diploid seed parents, giving you the opportunity to select some excellent triploid offspring of your own (maybe even fertile ones). The reverse cross can also probably work, but maybe with a reduced success rate, at least in my experience.
Here is a previous thread where David wrote about this very subject:
Stefan