For the most part, yes. Some fragments survived, but the majority of what we know about the pre-Socratics has been filtered through later doxographical works. While it certainly isn't optimal, together there's certainly enough of an understanding of the majority of the pre-Socratics to discuss them in a philosophical context without relegating them to Classics departments. Particularly given their relation to later thinkers. If you're interested, this article is an interesting place to start:

http://plato.stanford.edu/entries/doxography-ancient/