It comes down to competitor and promoter preference. In the case of WSM, that stuff is allowed but it needs to be covered up. WSM is pretty much an advertisement for Met-rx in the eyes of TWI/IMG (the media owners) so advertising competing brands or other equipment is a no-no. Some guys don't use gear even when it is allowed. Savickas and Shaw didn't use deadlift suits for the max deadlift event from WSM 2011 and they were number 1 and 2.
"Strongman is stupid."
- Mike Jenkins