Not a complete solution, but ...
We allow importing of objects into the WS via the config option allow_import_file_extension sym, mat, txt, stp, igs, dip, dop, and so on. If your users are using this option to import non-CAD objects into their WS, you may want to put the option in the config.sup file to prevent them from adding the objects in the first place.
When these files are imported into the WS, they show as "CAD Document" in the WS [when mousing over the object type indicator icon], and once checked into the CS, they show as simply "Other". In both cases the icon is the same as you have shown. If I show the information page for the object in the WS, it shows as "Other". If I recall correctly, in previous versions of Pro/Intralink (pre 10.2), the objects showed as "CAD Document Other" in the WS and CS, but I cannot confirm this.
I was not able to find that icon in the attribute manager, or the type "Other".
Pro/Intralink 10.2 M030
Creo Parametric 3.0 M030
Regards,
Dan N.