In settings for media gallery in configuration tab it's possible to specified FULL Html format for text. The problem and I don't know if it's a bug or by design, when you create or edit a gallery it's not possible to have by exemple Wysiwig with TinyMCE. You have to input the full code manually. It would be nice to be able to use the input format setting for the main core who is normally available when creating a blog or article node. Even if you go to structure for the content type gallery we are not able to modified the gallery description field, it says it's lock !