The current Image Sequence renderer for VP9 supports bmp, dpx, exr, jpeg, png, tif, and wmphoto.
Be aware that this tool will apply PAR correction. You don't get a choice to turn it on or off. It might work to your advantage or it might work against you.
The DebugMode Frameserver can also export image sequences in jpg, png, tiff, and bmp. The bonus is that it does so without PAR adjustment. This also might work to your advantage or it might work against you. Also, the DebugMode frameserver is free and done out of the goodness of Satish's heart, so it might not be bug-free.