GPL doesn't count "Application Service Providers" as distribution, but does not prohibit to do so and to share/publish the combined/modified source code; It is just silent regarding SaaS, meaning that it seems that the GPL does not conflict with the EUPL on these points. And the EUPL (art. 5) compatibility clause states that, applied to a combined derivative, the compatible license will prevail in case there is a conflict with the provisions of the EUPL. When no conflict exists...