Can you provide more information on whether the results of ORS analyses using geographic coordinates are reliable, and whether there is support for using projected coordinates during matrix computations?
Reliable in what regard, generated routes and isochrones are always approximations to reality. Wether they are reliable depends on what you are using the results for and wether you are calling the service with “correct” parameters. Maybe read up a bit on what osm tags we use for the different profiles and the travel speeds we set internally and decide afterwards, whether this is reliable enough for you.
The API itself only takes WGS 84 (EPSG 4326) coordinates as input. If you are using our QGIS plugin, coordinates should be converted properly from the CRS you are using.