Yes Efteling uses the same uniform across the park, even the major rides don't have themed uniforms. There are some rumors this ride wil have themed uniforms but nothing has been confirmed. And about the steampunk uniforms, this ride has nothing to do with steampunk.
The idea behind this non-themed-outfit is that every visitor immediately can see which people are employees of the Efteling and which not. Also you can't see where someone is working, so for every visitor is the employee the same (from vacation worker until manager). So the idea is you ask easier questions to them.When you look at Phantasialand, you know that employee belongs to that ride so you don't ask him/her (as easily) of there are any lactose-free-menu's available in the park.
This is the outfit for the themepark (left women, right men). In the hotels they have the same outfit but in other colors!