In ArcGIS 10 it is now possible to add a custom GDAL based driver DLL very easly in ArcCatalog: Customize->ArcCatalog Options->File Formats->Advanced->Add new Raster Format This function automatically copies the DLL to the correct directory and registers the DLL for a specific file extenstion in the rasterformats.dat file.
This works great for a user who installs a new driver manually. As a software provider we face the problem to automatically install our driver on a system. This must be done in an automated setup and is challenging because the DLL file must be copied into the ArcGIS file structure and the rasterformats.dat file must be changed, too. It would be much easier if ArcGIS provides the manual workflow from ArcCatalog as script or other automated process tool which can be used in the custom setup process.