Is iSTAR Fusion capable of saving panoramas in OpenEXR format?

At present, iSTAR can capture a range of up to 9 exposures (depending on product model) which can then be processed using Exposure Fusion to a single JPEG 8 bit panorama.

You can if you prefer extract the source fisheye images and process these in a 3rd party stitching application such as PTGUI, which supports the export to 16 bit HDR formats like .exr and .hdr.