I was going to say the same.

Never any problems or hassle with security at DXB.

You could either go Emirates to JFK then take a domestic flight onwards to IAD, DCA or even BWI (depending where you need to be in the DC area) or pick-up the United flight non-stop to Dulles.

I've never taken a US based carrier ex-Dubai - I would suspect security at the gate will be a bit more strict with the United flight. I don't know if they employ a company like ICTS - I have only dealt with Emirates Security at the gate for flights bound to the US.

You could also look at Singapore Airlines - CMB - SIN - LAX (or EWR) and then hop a domestic flight to IAD. SQ operates a non-stop on SIN-LAX and SIN-EWR, plus there are the SQ services with a stop.

Edit: Any way you can route via AMS? AMS is a great option going through Europe if it is a choice.