No problems in single mode. No problems at all really, apart from this.
My friend makes the server and his addons work. I will make the server next time to see if that’s the case.
In multiplayer, I can see the Stacker Tool and Explosive Entities Tool listed amongst Tools and all the weapons are displayed in their boxes in the menus.
I can see the name of the tool on the tool gun when selected if it was used previously in single mode, but it will be unresponsive when clicking.
I have downloaded the Nuke Pack, the Melonium gun, RPG-7 gun, Stacker tool and the Explosive Entities tool. That’s all I remember at least, or what I want to be able to use. 
I downloaded the gm_perfectz_world_v2 map too, and that works fine for both of us.