I've been datamining the Internets for the past few days and I return with UPDATES!
First, something that should've been done a while ago: the entire GDI Style Guide for Tiberium has been digitized and uploaded to the Wiki for your perusal.
Second, attendees of the Games Convention in Leipzig might recall him, here's Ralf Zillmann's Commander Simon Drake, a staple of the Tiberium Wars release party in Cologne and the two Games Conventions in Leipzig.
Last, and probably least, data mining uncovered a ten year old iteration of something called the C&C Bible, penned by John Scott Lewinski. While the bits of information relating to characters appearing in Tiberian Sun sound quite credible and can be assumed to come from design documents, the Scrin background provided is too incredible to be anything else than the writer's own creativity and shouldn't be taken as any kind of source material.