Yes, you should be able to customize any promotion on your social media with your brand image. First of all, so that the users know who promotes or organizes the action. Secondly, because one of the main objectives of promotions, is to achieve brand visibility. In comment-based social media giveaways, it's important that your logo appears on the post image. In promotions that are shared on social media but hosted in a microsite, it's much easier to customize all the elements. From texts, the logo on each page, to the corporate colors, etc. All the Easypromos game apps, for example, allow introducing many elements to make them aligned with the brand image.