Yes there is a requirement to work with the vendor format. For instance, TCGA (The Cancer Genome Atlas - a large dataset of 12k+ human tumor cases) has mostly .svs files (scanned with an Aperio scanner). We tend to work with these formats as they contain all the metadata we need.

Sometimes, it happens that we re-write the image in a pyramidal TIFF format (happened to me a few times, where NDPI images had only the highest resolution level, no pyramid), in which case COGs could work.