Do you study GM games based solely on openings you play?

Actually "not completely". Any player should learn to play any kind of position, with different pawn structures. That is mainly to help to build your chess itself. There is nothing wrong with playing through those games to build your opening repertoire, actually is a good idea if you are someone with little time to study. But you must to be precise, what you want to study, openings or master games? You need to carefully isolate those two things, because studying games will give you ideas, common patterns, plans, strategies, etc. But with openings is anoher thing completely different, when you study certain opening you need to understand why those moves are the best, and why to play certain positions in a very specific way. To understand that you need to see notable games where a player failed to play like the book said. And that is a very hard work than just see or study master games. Is a good idea, for example play the games with an opening book and an engine, but after you have analysed the game. When I started to study the KID and the Slav and Semi-Slav, I read the "Starting out" books to understand the games, and nawadays is tha I'm "studying" the theory. You always need to study master games to find new and useful ideas yourself to apply in your games.

giant wall of text alert ^^

I do that. If any kind of position can arise from any opening then just studying them based on the openings you know will eventually get you those same positions, but you will also know how to derive them. Plus, you will be focusing mostly on the types of positions that are most relevant. It's so much smarter, in my opinion, to study GM games from the first move to the last based on your opening unless it's one of those incredibly brilliant games everyone should know. I'd do that even if I was studying Tal (I'd rather be accurate than chaotic, so I don't), because it's about how you get there as well, which is especially important for someone like you, as a Tal student who doesn't know how to stir up the hornet's nest is a bad one in my book.

You'd like to study a great predecessor of the game to expand your knowledge base - but only the parts of his career that fit into your current knowledge base? That doesn't make sense. :) Is that ego trying to fit him into your box, where you should be trying to mold yourself into his?

I hope you're studying it via Tal's book (one of the alltime great ones).

I don't know if this thought is right, but I'll try to clarify here:

Ego is self-importance. It would make you a better student of the game if you put aside your own ego in order to learn. The original question seems to be asking whether your own knowledge (in the dutch defense) is greater than what you would find in the rest of Tal's games that are not the dutch defense.

If you decide that your own knowledge is greater than what you might discover on studying Tal's games, then you have let your own ego get in the way of learning. Hope that is more clear!

#9 - this seems like an odd way of looking at it. It's not that there's nothing to be gained from studying games with openings that you don't play, but seeing how a master plays a given opening seems like a definite benefit if it's an opening that you play too, and given limited time for study, why not get both at once if you can?

Incidentally, this also seems like some argument in favour of playing mainline openings rather than sidelines - like, there's obviously a lot of theory in the Open Sicilian for instance, but you'll also pick up a lot of the ideas by osmosis just because it comes up in so many master games.