Yes you can run a freewheel on both sides. The different hubs were made for different audiences. The trackies want a hub they can gear for two different events or to ride to and from the track. The mixed hubs are for people who want to try fix gear but have a freewheel bailout. I'd only known of mixed fixed-free hubs until I asked the Portland fix gear guru if a fix-fix existed. Now I have a bunch of them.
As many of you know, I am a fix gear die-hard. My last singlespeed was my UO-8 up till 1976. Then I put on a fix gear wheel. Never looked back. I've had at least one fix gear in my stable since then (currently 3 of 5 bikes. 2 have fix-fix hubs. Have all the cogs from 12 to 24.)
A little off topic but the one hub that didn't pan out for me was the beautiful fix-fix Miche of their high end boxed set. Not enough available lockring threads using a very track-common Eurasian 1/8" cog. Stripped both sides. Rode Cycle Oregon last fall with no lockrings, (Well, one was on but only for decoration.) As others have said, if you are aware, ride smart and use brakes, not an issue. I blasted down the north entrance to Crater Lake on a 42-12. Only issue was the aching cheeks from the ear-to-ear grin. My all time favorite fix gear descent. And that is a great gear for it.
I've had zero thread issues with the considerably cheaper Miche fix-fixes Some of mine now have many thousands of miles and lots of cog swaps. I do wish their axles had slots with tabbed washers. The lock nuts unscrew. If you sock the hub nut down on the unscrewed locknut, you break it but you won't notice until the broken nut falls off next time you flip the wheel. Never been a ride ender,, but still, Miche, you can do better.
Ben