I have been FL sizing and decapping my brass before cleaning it in my US cleaner.  Is this ok?

I wouldn't.  Your going to skuff the hell out of your dies and your brass.
Decap, wet tumble, resize.

With my brass it would be OK because my brass never hits the ground.

With your brass, I don't know.

I wouldn't do that either it will scratch the dies up. If you want to decap before tumbling get a lee decapping die.

I always run my dirty brass through the wet tumbler for an hour or so to knock the dirt off prior to handling it whatsoever

If you burr the sizer die, it'll scratch every piece of brass from that point forward.
At 50,000+ psi, I wouldn't want to create a potential weak point.

Just clean em first

Definitely use your US on the brass before sizing. They will run through your dies smoother as well as add life to your sizing dies.

I've been doing it this way for years

Contrary to claims I've heard my dies have not fallen to pieces. In fact they have to discernible wear or scratches whatsoever.

Now I'm talking about regular brass that been fired and hit the ground and picked up, not stuff that's been stomped into mud or anything. I throw really nasty stuff into a separate container and when I have enough I run it in walnut for a few minutes.

The part in red is debatable and the part in blue is impossible

Over the past 30 years I've done it both ways... without cleaning brass before sizing and cleaning first.
I could feel the difference in how cleaned brass fed smoother through the single stage press compared to uncleaned brass. I use steel dies with pistol brass and always lube the cases.

I don't have to lube as much with clean brass either and could skip lubing a case every so often as there is enough lube on the die for the un-lubed case to feed easily. Couldn't do that when I was not cleaning brass before sizing.  

Steel dies do wear... and dirt and debris act as an abrasive to speed the process. Carbide dies not as much.

Now I wet tumble after decapping, then dry tumble with some nufinish added to the media. Lubing the case is still done but sparingly since it's even smoother through the sizing die.

I now feed 40sw and 45 through a push though sizer after the sizing die to remove any bulge at the base. That can take a lot of force on the handle sometimes. I've never tried uncleaned brass through the push through die, but I can imagine it would be even more difficult to press through because of added resistance.