There is currently only syntax support for Expect. The filetype is set when the filename extension is *.exp or from the appropriate shebang line in the expect command file.
There is, however, full support for TCL so I've attached ftplugin and indent plugins for Expect which just source the corresponding TCL files. I'll send these to Bram for inclusion in the distributed runtime after I have a think about whether there's a better way to do it.
Regards,
Doug