Don’t assume anything when it comes to ploidy. Some of the most fertile cultivars I have worked with are triploids, and some of the most INFERTILE are tetraploids. Triploids can be very useful parents.
Golden Angel is a triploid, and yet it readily produces viable seed (and pollen). Out of Yesteryear is a cross of two tetraploid parents and yet it is a triploid with extremely fertile pollen. I crossed Sheri Anne (tetraploid) with Out of Yesteryear (triploid) and the resulting seedlings were a mix of tetraploids and triploids. Ploidy in roses tends to be very fluid and you shouldn’t assume that you’re going to get any specific result when mixing ploidies. Just try some crosses and see what you get. Take notes.