It is not based on vscode as far as I know, but it does use the vscode language servers and snippets. Regarding splits, if you set "tabs.mode" to "tabs" it will behave just like regular vim tabs, so each "tab" is just a neovim instance that behaves exactly as you would expect it to. There is a feature in development that creates a GUI "tab" for each split[1], but I found it difficult to use so I'm sticking with native vim splits for now.

[1]: https://twitter.com/oni_vim/status/969315834626695168