Yes they will be compatible, they are compatible now. Issues are, materials are not perfect, colors are off, had to set two-sided for cloak to make it not invisible from the inside. But UE animation retargeting works smooth here.
If I compare those characters with the one I made with Mixamo, those have much cooler gear/cloths, and look more unique, more human like. Problem, it’s not free, but if you for instance are in need of some people to fill the main street in your game, then even the current trial software is a good choice.
Also if you export with the trial 3DExchange version, disable exporting “Motion”, since that counts toward your trial export limitations.