That isn’t correct. A server’s pure status has nothing to do with PB. Here is the relevent section from RTCW & ET 4 Newbies
Why don’t I see the skins I just downloaded?
First, make sure that you’ve installed it to the right folder. If you look in your [gamedir]/main/ folder, you should find the file in there with a .pk3 extension. Make sure it really is .pk3 and not .zip or even .pk3.zip. If your file is in the right place and is named correctly, you might just be playing on a pure server that doens’t have your custom skin pack. So, What is a pure server?
Pure servers only allow you to use a pk3 file IF it exists on the server AND your copy of the file matches the copy on the server exactly. This is to prevent people from creating new files that help them cheat (e.g, bright green Axis skins etc). This means that either the server you are on doesn’t have the file in question, or there was some discrepancy between file versions.
For example, if you have the female classcoat skins and the pure server doesn’t, you won’t see yourself as a female. If both the client and the server have the female classcoat skin pack loaded, BUT your file is different from the server’s (e.g., because you wanted to swap out some of the sounds), the entire pk3 will be invalidated and you will not see yourself as a female.
You do not need to have the same custom pk3’s as the server in order to play. What must be identical to the server are the basic game files (e.g., Pak0.pk3 through Pak2.pk3) and the map file
Custom skin, model, sound, crosshair, or other maps (other than the one currently being played) should have no effect on you being able to play on a pure server or not.
If you know the server admin and you absolutely have to have that skin pack activated, ask the admin to put the skin pack on his server.