If you are a super admin who enters the hotspot, then you should be able to enter all kind of HTML in the description. However keep in mind that the default editor is striping html tags. Try to disable the editor (globally on the site) and then enter your html. If the html is not stripped, then you have the issue. Also it is possible that the email cloak plugin is modifying the output of hotspots. Try to disable that plugin as well.