Yes, it is allowed and HEM supports the Merge network. If you have any issues setting it up or with it in general, I would recommend getting in touch with HEM support.
Here's some info I posted in another thread. I had some issues with HEM and Lock when I first played there:
I had some issues when I first played at Merge.
1) Make sure your hands are indeed saving. I had to re-check the option several times before it actually saved.
2) Go to import tab, add import folders, auto detect. If it doesn't for some reason, point to the folder - it's in program files and then handhistory like FTP.
3) if your hands are importing but you're not getting a HUD, open your table manager (pops up when you click import). The second tab at the top is table, first option is table finder. This brings up a box with a red box with an X in it.
4) highlight a table name, then drag the X to the actual table, then click ok.
Those steps fixed my issues with importing and HUD.