Does a bacterial swab on a bump or lesion finding pseudomonas aeruginosa mean it requires treatment, even if the swab says light growth?

Yes. This bacteria is dangerous. The bacteria is aggressive and can be difficult to resolve. Immediate attention is required.

This depends on symptoms and other evidence of infection. It's not abnormal to have Pseudomonas (and an infinite number of other bacteria) on normal, healthy skin, and positive culture by itself usually doesn't require antibiotic treatment. If your doctor believes an active infection is present, it may or may not need treatment, depending on other bacteria present and the nature of the problem.