Officially, no. Unless explicitly given permission in writing from TPCi, you are not technically allowed to use any official images, including Play! Pokémon logos, Pokémon League logos, or set artwork. In some cases, notably for Prerelease events, TPCi provides images that may be used for event promotion.

Never, ever, under any circumstance, use fan-art for graphics. Do not use character art unless provided by TPCi. Do not use TPCi intellectual property when creating trophies, prizes etc for your event. It is imperative that a graphical standard is maintained across events and that fan art is never utilised.
Kay Dyson, The Pokémon Company International

Note: Many Professors do use official logos and artwork without permission, however, and have not been disciplined by TPCi for doing so. However, we cannot promote this practice, and doing as such is entirely under your own risk.