This really depends on the device: both make devices in a variety of protocols, though the ones you'll see people mention around here are Zigbee. Those will work on Hubitat without their hub/gateway, but keep in mind that only the Sonoff devices are officially supported on Hubitat. See those model numbers here: List of Compatible Devices - Hubitat Documentation. Many Xiaomi, including Aqara, devices can be made to work with a variety of custom drivers you can find on the forum (though at least some require you to be careful with how you build your mesh; see this thread for more: Xiaomi & Aqara Devices - Pairing & Keeping them connected).
Sonoff has a lot of Wi-Fi devices that will not work natively, though some may work via community drivers and may or may not also require custom firmware to be flashed to the device. Xiaomi has lots of products in the same boat, though I think all of the Aqara ones I've seen are Zigbee except the camera (which again has no integration). So just make sure you check your specific product first.
On a hub-related note, there is no integration for either of these manufacturers' "hubs" (bridges/gateways) into Hubitat, so the only way you can use them is by directly pairing them to Hubitat instead--or at least the only way without some workaround, like putting the Aqara devices into HomeKit and using some automation there to mirror things between it and Hubitat, which could theoretically work for many kinds of devices but probably isn't how you want to start off if you're buying new devices.
