I have recently umm downloaded the Dragon Cookbook from Chessbase. It is filled with human and computer games in the dragon. The thing is, are previously played computer games allowed to be seen in correspondence chess?
On chess.com, use of books and game databases is allowed. Use of engines and tablebases is not. Your book is either a book or a game database and therefore fine.
There are also sites that don't allow any outside help (no books, no databases), and on the other hand the ICCF (the offiical FIDE-affiliated Correspondence Federation that is also completely online nowadays) does allow engine use, so it's best to always check the rules of the actual site you're using.
It is not illegal to view and use previously played Chess games, some people even use Chess Analyse programs while playing on (for example) the internet. However most websites do not allow you to use programs to gain benefits over other players, including but not limited to analyzers.
Ofcourse it is allowed to study previously played Chess games, you can even learn a lot from them!