Just as the title of the questions says, is there an LuaTeX analogue to XeTeXinterchartoks?
I hope so, but the answer is no.
\XeTeXinterchartoks mechanism heavily to implement
xeCJK packages to support auto font switching and other features or CJK. But we cannot transplant them to LuaTeX.
Now the same feature in LuaTeX (zhfonts module of ConTeXt) uses a totally different mechanism to implement:
pre_linebreak_filter etc. If you want to do similar things in Greek, I hope it would help.