As an anecdotal point, when I played 40K tournaments a lot back around the 2e to 3e transition.
A: It never said anywhere but I never saw anyone bring a non-GW figure. They were sponsored events, so I’m sure they’d have asked the figure to be replaced though.
B: I used several Rogue Trader figures in my armies (late 2e through late 3e) and never had a bad word said about them by players, staff or visitors from GW.
Nordic Weasel Games