Yes, links to fansites that are not a part of the fansite program are generally legal on TibiaQA. Of course, this excludes sites that focus on illegal activities such as botting or that are designed to hack into other players' accounts. Clearly off-topic links are also not allowed - like a link that has nothing to do with Tibia and the asked question.
As of today, links to TibiaFrags are totally fine if they help answer the questions in any way.
Hope that clears it up!