Roon currently does not support ISO files, nor would there appear to be any plans to do so.
Several ISO to DSF converters exist and roon does support DSF. However ISO files are normally compressed by DST so when uncompressed/converted to DSF there is a significant jump in file size. Although disc storage is very cheap these days there are many scenarios where the increased disc storage is a considerable inconvenience or just impractical. One example is storage on a work or travel laptop where the options may be limited. Consequently there are several discussions/feature requests for ISO support.
Roon does not support Wavpack (.WV) either. However Wavpack 5 now supports DSF compression. So this is a feature request for DSF compression via Wavpack. The details can be found here: