Hey Young Money (K20),
Yep, you need a spring compressor to relieve the tension on the spring itself while on the strut assembly. The reason for this, is if you remove the strut's top nut off the unit without the spring being compressed down, it will fly off because of the pressure the spring is putting on the top housing.
So, the short answer is yes, you need the spring compressor to be safe. You can rent them from an auto parts store, and when you return it, it's usually a full refund of your deposit. Check with them to make sure!
-MCQ