Hi,
If your WMS has a geographic coordinate system assigned to it Raster Manager should be able to do the unit conversion from metric to english. If this is not happening maybe this is a bug.
Also Raster Manager has the ability to reproject the WMS to the GCS of the model (MarshallMN-F). Some information about reprojecting a raster can be found here : communities.bentley.com/.../raster-reprojection.aspx
Finally if you could send your .xWMS I would be happy to investigate further what is going on.
Thanks,
Mathieu