Wow, what an interesting idea.
No, I don't think that Roland and the Crimson King are the same person or twins or anything like that. They exist in the same universe at the same time. We could think that Crimson King is from another universe and he used to be Roland once somewhere far far away... but it's such a strong guess I don't think it stands. No evidence.
I don't think the fact that they both are the fathers of Mordred can be called and proof either because in a world where people can hide in someone's mind (Mia in Susannah's) be pregnant there and then like a fax machine leave the body to deliver the baby... it's not a big thing to make two sperms become one.
Anyway Roland isn't that type of person who just goes mad. When he was fighting with the memory of Jake (there was a boy there was no boy) he could hold on for long. To sum up for me it's out of the question but it's a damn interesting question.

It's true we don't know much about the CK in the DT books but you can find lots of information about him in the comics.