While it is technically correct, it doesn't read well and would be awkward in speech. "Less well" equals "worse" in most contexts. The sentence "In his studies, he is worse at art than science" would read better and highlight that the writer wants to make a comparison between art and science. "Less" is typically only used before "good" if a writer is using "good" as a noun. For example, "The doctor did less good for the people of the village than she had hoped." In common usage, however, it is very rare for a native English speaker to say "less good" or "less well" as opposed to "worse." I hope I helped!