Yes. However, if you use mutliple devices on the hub, either the hub or the external USB devices must have their own power source. The power available from the USB port on the SMP is limited.
I think I’d add that USB hub support can be flakey.
Find the right one and you should be fine.
One thing to note - it’s better if both the hub AND HDDs are both powered.
I have a set up away from home with a powered hub and 3 HDDs, two of which are powered and one that isn’t. It worked fine at first, but then started to drop the un-powered HDD.
At home I’ve had a hub with 3 x 6TB HDDs attached, no problem.