Solution:
Yes – you are safe to just use array($this, 'init');.
What this is actually is, is a “callable” in PHP. It will be invoked using call_user_func() or call_user_func_array() (internally inside the add_action method).
PHP’s official description of this type of callable:
A method of an instantiated object is passed as an array containing an object at index 0 and the method name at index 1.
You can read more about callables here.