I'll answer my own question in case anyone is bumping their head on this. I added MsgBox(fmDoc.fullname) to the loop ( as below ) so I could see what names were being reported by vb. Local files included the file extension ".fp7" but hosted files did not. So I'm now able to execute a script in a hosted file.
For Each fmDoc In FMDocs
If InStr(LCase(fmDoc.fullname), LCase("ExecuteScanScript.fp7")) > 0 Then
' this is our file, run the script
fmDoc.dofmscript("Execute Scan Script")