I believe the technical answer is yes, it still could be, but in practice would be very rare, and would certainly cause them to be hesitant about an MS diagnosis.
It would also depend how many lesions in the spine, and where. If there was just a single lesion, I don’t believe this could ever be diagnosed as MS, as it doesn’t satisfy the McDonald criteria (evidential rules for diagnosis).
Even if there were two or more lesions at quite different parts of the spine, it usually still wouldn’t be sufficient for diagnosis, as there needs to be proof they got there at different times - which there couldn’t be, from a single MRI.
So my feeling is that even if your spinal MRI showed an abnormality, it won’t be sufficient for an MS diagnosis, no.
It might be the difference between discharge and/or referral to another specialism and keeping the book open to see what happens, though.