Yeah, I had the original Key chain games, I actually just got Digimon World for the DS. It mentions DATS. but since it also mentions File island and "Azulongmon" I thought it was based in the season 01-02 universe.
And the digimon Cardgame actually exists Atlan, the cards look as advertised in Tamers, though they came out during 02 if I recall correctly.
Also if we're talking about Digimon games that were awesome. The wonderswan and WS Color had a couple of great games that predated Digimon world by a rather lot. I happen to have Anode and Cathode tamers for the WSC there's the basics of Digimon World right there.
As for the games, they've always been really really well integrated with the series. Ryo from season 03 is the star of the Wonder Swan games (which were pre-Tamers), and most of his backstory is actually pretty reliant on those games. There was a Manga (V-Tamers I think it was) that was parallel to all the series again. and even through the various incarnations of the Series and games there have been clues and links that all the series are if not in the same universe, than in different "Quadrants" of the same digital world.
There's a definite Lovecraft influence in a lot of the series too. That Dark Ocean thing heavily hints at lovecraft's dream world stuff, and had "Dagomon" (from Dagon though looking a lot like Cthulhu) and "Divermon" (which look a lot like descriptions of the deep ones).
It's really one of the most well thought out series I've seen. with a whole hell of a lot of culture references that even now I'm just beginning to get all of.