First of all why did you rename the game
Second of all, why don't you fix the game so it can run on more PCs?

First: "Blood 2: The Blood Group" was the name of a double pack release containing Blood 2 and the Nightmare Expansion in stores, same thing with the One Unit Whole Blood pack for the original game.

Second: GoG really cant "fix" the game persay as they dont have access to the source code and such things sadly.

Ist it Possbile to run that game on W7 ? Or i purchase it without any sense?

It is very possible, but there's no guarantee. I and several others I've talked to had no major issues in playing it on Windows 7.
When a game on GOG isn't officially supported for a particular system, that doesn't necessarily mean it will absolutely refuse to work, but rather that it failed some of GOG's compatibility tests. So, it's a bit of a gamble, as it means GOG won't be able to offer you technical help or a refund if the game does run into severe issues on an unsupported system.

Also, be aware that Blood 2 is just generally a really, really buggy game. It'll do all sorts of weird stuff and is rather prone to crashing, no matter what system you're on.