I don't have expertise in this field to answer this question definitively. I studied General Relativity, so I have more expertise than you do. But, unlike you, I know that in areas that I don't have enough expertise I have to either do more study (which would involve going back to the Univesity or at least reading papers and doing math).
Almost all of the people who have done this work accept General Relativity as accepted fact. They know more than I do, and they know more than you do. I at least have the ability to understand the mathematics and read the papers.
Sorry, but there are no short cuts in science.
That being said (and now I am giving you my opinion without having specific expertise)...
My understanding is the General Relativity does not depend on dark matter. It is possible that there is some other force, that fits into the frame work of General relativity, that we haven't discovered yet.
So to answer your question... in an area I admit that I am not an expert in... I believe that dark matter is not necessary to confirm General Relativity. There is enough evidence that confirms General Relativity without the cosmological phenomina that suggest dark matter.
Hopefully I am being a good example for you. I admit when I don't have expertise in someting... rather than running to Google to support whatever I choose to make up.
If I choose to finish my PhD and specialize in cosmology, then I will have the expertise to answer your question definitively. But until this happens, I am in the same boat that you are in, and it is foolish for me to not listen to the people who have actually done the work.