First, GDNative objects are actually a wrappers for an internal Godot's object instances. So you cannot "override" its unexposed core behavior, for this you need to use a module.
As of normal use of callbacks like _init
, _ready
, or whichever ones given type is supporting, all GDNative classes (incl. MainLoop
) are resembling its GDScript counterparts, so yes, it should be possible.