do observant jews who are not chassidic regard the Tanya as 100% Truth? What about Samach Vov? What about the other older main chassidic texts?

ב"ה Shalom All writings of true Torah scholars are holy and should be regarded as such. However, not everyone who is a Chassid reads all the works of all the Chassidic leaders, on the one hand. On the other hand, there are many non-Chassidic Jews who also study the Tanya and other works of the same author, Rav Shneur Zalman of Liadi zt"l. The Tanya is high level book and not meant for everyone. In regard to your other questions, I can try to be more helpful if you are more specific. "Samech Vav" is a fundamental work of Chabad thought, but I'm afraid I'm not familiar with it. All the best