Yes, artillery tends to make a big flash and produces a lot of smoke and dust when firing. Various means can be taken to reduce the visibility of said blast (for instance, special "nighttime" loads produce less flash, but more smoke) but in general anti-tank gun manuals tell you to prepare several reserve positions and relocate after firing. An anti-tank gun's only defense is its small size, and if you keep shooting from the same position you will be spotted eventually.
Specifically about the 6-pounder, there may not have been a 30 feet long "blowtorch" but there was definitely significant flash and blast when the gun was fired.
Sadly, I don't have documents towed 6-pounder flash/blast, but I do have some on the tank version with the same ballistics. Trials in a Churchill III and Crusader III tanks showed that the flash was significant enough to blind the gunner temporarily such that it was impossible to correct fire at a range of under 700 yards as you wouldn't see the tracer or the impact of the shell. There was also a lot of dust kicked up by the shot, even though the barrel was higher up from the ground than it would be on an anti-tank gun. Blast from the longer Mk.V gun was powerful enough to tear off the fenders and damage stowed instruments.
Unfortunately, I haven't seen a document that describes the amount of snow and vegetation disturbed by the blast, but I think it's safe to say that the 6-pounder, like any powerful anti-tank gun, produced enough smoke and dust when fired that the crew would be wise to relocate after firing.
Sources:
Library and Archives Canada, Canadian Military Headquarters, London reel T-17473 image 550
Library and Archives Canada, Canadian Military Headquarters, London reel C-5778 image 585
http://www.tankarchives.ca/2014/01/soviet-at-instructions.html
http://www.tankarchives.ca/2015/08/anti-tank-defense-manual.html