I'm going to assume that when you say 'valid', you mean 'true' given the rest of the words you wrote, not in the title.
I would say that yes, ideas can be unscientific AND be true. If someone comes up with an idea but does so in a way that is completely divorced from any of the many "scientific methods", they could be right and be unscientific.
Being scientific doesn't make an idea true, being unscientific doesn't make an idea false - BUT being scientific is clearly and unambiguously correlated with being less wrong than people who do not try to be scientific - at least in the realms of inquiry science has proven itself effective in, like medicine.