data protection and copyright are two different things, neither of which apply to your situation. According to the EULA any and all assets created and used in game become property of Rockstar anyway, including all mods.
As a general rule, if the mod says you're okay to use it in FiveM, you can use it on your server. If it says you can't, then don't, and if it doesn't specify or you're unsure, message the creator and ask permission.