I'm writing plugin for Rust and it became necessary to connect third party dll unrelated with Oxide. Maybe who know how i can make this, because when i try load plugin in rustAdmin i seeing message that Type or namespace "could not be found dll being connect by me"

Did you loaded it to Managed folder?

Yes, but that did not fix the error

Error while compiling: VkRust.cs(19,7): error CS0246: The type or namespace name `VkNet' could not be found. Are you missing an assembly reference?

You'd have to add:

// Reference: DLLName

To the top of the plugin.