Epic has just released the patch notes for version 7.30 of Fortnite on mobile, and they happen to include support for Bluetooth gamepads.
Most controllers are supported on Android, including Razer's Raiju, the Steelseries Stratus XL and Microsoft's Xbox One controller, while iPhones and iPads are limited to accessories that follow Apple's Made for iOS spec, like Steelseries' Nimbus and the Gamevice grip. Additionally, Fortnite will automatically disable your phone's vibration when a supported controller is paired.
The patch also introduces 60Hz mode for select Android models — specifically, the Samsung Galaxy Note 9, Huawei Mate 20 X and the just-released Honor View 20. Previously, the iPhone XS, XS Max and XR were the only handsets that were optimized to run Fortnite at a full 60 frames-per-second. All other Android phones, as well as older iOS devices, are still limited to 30 frames-per-second.
You can read Epic's full patch notes here.