You're going to have most of the game content (models, textures) on the "development" PC anyway.
Unless Valve has finally opened up and included a utility to extract and create GCF files then no, the game content doesn't need to be on the development PC and in fact, couldn't be used even if it were. That has been the problem with the Steam version of Half-Life and Counterstrike for over a year. Valve has provided absolutely no tools to make use of the content such as textures and models in the Steam versions of Half-Life and Counterstrike due to all of the content being protected away in proprietary GCF files. Yes, one guy did reverse engineer the GCF format more or less so that this content could be extracted and used but it certainly was not with Valve's blessing. So, if all a person had were the Steam versions of Valve's games, they would not be able to create maps which use the game's existing textures.This comment was edited on Dec 4, 17:27.