All I can say is that this depends.
I’m probably the poster child for what not to do.
I have the following, all mounted on a side wall, all within a foot of each other, and I have no issues to speak of from a usability perspective.
-external 2.4G wap antennas
Not recommended, but it’s working for me.
They will conflict somewhat, it just depends whether they cause enough trouble to affect your QOS (“quality of service”) for any particular devices.
Best practices say each of them should be at least 3 m from each other, but a lot of people just don’t do that and don’t notice any particular problem.
There’s no problem with trying and seeing what happens, just be aware that you may want to space them out.
The Hue hub allows you to change from one zigbee channel to another through their app, which could help reduce interference. The SmartThings hub has its zigbee channel set at the factory and cannot be changed afterwards. Ideally you want these two on Zigbee channels that are separated from each other as they actually communicate with each other over the LAN not Zigbee. So you are running two separate zigbee networks.
You didn’t mention your Wi-Fi router, but it can also cause interference as Wi-Fi and Zigbee bands overlap in the 2.4 range. Boosted 2.4 Wi-Fi is a particular problem. So it’s good to put as much as you can on the 5.0 band. However, the harmony only runs on the 2.4 Wi-Fi band so you’re stuck with that one.
Just be aware that if you boost the 2.4 Wi-Fi to get a better harmony connection you May then start to impact your Zigbee connections, particularly for any battery powered sensors which tend to be the most affected as they typically have the lowest power signal.