It's possible and it's allowed. But it tends to have Lag in the current Roll20 (especially during the uploading, also sometimes while using the map). However in "Jumpgate" the upcoming new version of Roll20 that is currently in Beta testing, there will be better support for animated maps. If you can wait a matter of weeks or months, or if you want to test converting a copy of your game into Jumpgate Beta, this probably has better support than the default Roll20. The most "native" ones that's most likely to work off-the-shelf, are the Animated Maps that they sell in Roll20 Marketplace, because those are already uploaded into a server, so you don't have to go through uploading/converting them.