Short answer? NO!
Taking a shower right before the spray tan raises the chances that there will be product left on your skin, blocking the spray solution from being absorbed property. The biggest culprits of this are razors with moisture strips, and Dove body wash/bars. You really shouldn't be working out hard directly before your spray either. Even though you 'll be able to rinse off the sweat, you will most likely still be sweating during your spray, which is a no no! Any of these actions could mean darker "blackhead" looking pores, streaky patches, or uneven color on your developed tan.
The best time to shower before your spray tan is ideally about 6-12 hours before your spray tan appointment. You'll want to give your skin time to dry, and get back to its normal PH level. If you get your spray while your skin is fresh from the shower you will still have water in your pores, and that could cause the tan to develop differently than it normally would.
Before your spray tan , you'll want to exfoliate your skin thoroughly using a chemical exfoliant, exfoliating mitt, etc. After this shower you'll want to avoid using lotion, perfume, and deodorant if you can help it!