I've only done hard science thesis papers, so some of this doesn't necessarily specifically apply to humanities.
Thesis statements:
a) address a specific topic.
b) takes a distinct position on that topic.
c) explains why research is actually even needed.
Addressing a) and b):
Thesis statements for scholarly articles (most often) require independent research and analysis. Therefore the thesis should be distinctly different in some regard if you are addressing a related topic or even specifically trying to disprove someone else's research. If you are only using their research, it's a summary not a thesis. Having a section dedicated to their specific research is perfectly acceptable. You need to state why it is relevant, what it shows, and whether or not it supports or contradicts your research. You can include criticism of the technique employed in their research and the assumptions they made. Obviously you need to cite all the data they collected as well as any specific statements within their paper. In the case you try to disprove them, obviously the thesis statement is distinctly different because it is contradictory.
for c)
Using the exact same thesis statement is acceptable when multiple independent research papers are trying to address a specific topic of discussion, as long as you clearly state what your position is on the topic and why you believe your research is even needed. But this then always relies on personal research and data collection to compare to other people's research. If you aren't using any of your own original research, and just stating an opinion that is the same as someone else, it contributes nothing to the topic at hand.
It is possible to write a thesis comparing and contrasting other thesis papers on a topic in which a great deal of research has been done. Often this is done if you think many of the conclusions are formed from poor research or you believe they don't address a specific point in a general topic. Your thesis is intending to prove that more research is needed, not to actually prove a position you have on the topic.
Summary for each of your questions since I'm not sure I organized myself all that well:If you take someone else's argument or even just their thesis statement?
Unless they have a really unique idea, there's not much that distinguishes a thesis statement or outline/argument of a paper.
Since a proper thesis statement is so specific, taking someone's argument will always be word for word and therefore plagiarism if you don't do original research. Their research should be included in 'why the topic needs to be addressed', so you'll need to cite them anyway.
Nothing word for word, just the idea, the concept?
Taking a concept from someone else's thesis will still make their research relevant to your's no matter what. Because of that it will be included in your paper anyway, and should be cited.
Or if you take an outline of their paper and then redo the research? Is that plagiarism?
In regards to an outline, if you mean simple format, it's perfectly acceptable to use it if you think it will help present your argument in a clear and precise way. But that is only in regards to organization, not any of their statements.
Another variation, what if you took someone's paper, reused their thesis, argument, even their sources, but checked the sources yourself, added a few more source or even a little extra argument? Everything still actually done by you, but pretty closely following someone else's paper? All your own writing, all your own source checking, but mainly a paint-by-numbers project. Is that plagiarism?
Yeah, I'm pretty sure this is plagiarism. But going back to why you write a research paper, what is the point of even doing this if you are trying to contribute to research done in a specific topic? Many class essays aren't really theses, that word was overly abused. They are more often a summary of research, showing why someone else's argument is valid.
Starting your paper with "Smith argues [thesis]
1" isn't a thesis, it's proving/disproving they actually did their research and made a proper conclusion.
Again though, I've really only done hard sciences.
If you want to discuss the specifics, feel free to post your subject.