The story makes it sound a bit sketchy. One direction and .63 mph faster? The veyron had to use an average of two directions correct?
Fast is fast either way.
But they are aiming for a proper goal at least-fastest around the Top Gear track. 
I've been following the Venom GT for a few years now. As far as acceleration and top speed it is in a league of it's own.
Think about this, the Veyron 16.4 SS set it's top speed run on a 5 mile straight, with a 150mph rolling start out of steep banking. The Venom GT did it on a 2 mile runway from a standing start, and it was still pulling when he had to brake. You are right, Guinness did not award the top speed record to Hennessey because they did not do a run in both directions, also more importantly they say you must build at least 30 cars to be considered 'production' and Hennessey only plans to build 29.
The Venom GT did get a Guinness record for 0-300kph (186mph) acceleration at 13.63 seconds.
It's all about power to weight.
Veyron 16.4 SS: 1200bhp and 4,400lbs curb weight. The P/W ratio is 1/3.6
Venom GT: 1244bhp and 2,743. P/W ratio is 1/2.2
The Venom GT has a bit more power, but more importantly is over 1,600lbs lighter. The Veyron very nearly weighs a
TON more.
The Veyron to me has always seemed like a heavy, over-engineered oddity. Like those Volkswagen engineers got some loopy juice and just went nuts. I mean a W16 engine, 4 turbos, 13 YES, 13 radiators?!?! All that complexity and added cost and weight for what? 1200bhp. Really... American muscle car, and drag car builders have know how to get 1500+bhp out of a small block Chevy or Ford V8 for decades. What I like about the Venom is it's back-to-basics simplicity. Lightweight body, twin turbo V8, super wide tires = go very, very fast.
I'll just leave this here for some final food for thought. From Goodwood a couple years back.
https://www.youtube.com/watch?v=0pE_WFWjsgE