From quick googling I found a PythonLibrary called pySerial which also works for IronPython and so within Grasshopper. It enables you to read or write to a serial com port. This way you can really simple read or write data to your ardunio from within any app. Haven’t tried it, but it looks very straight forward.
https://pyserial.readthedocs.io/en/latest/index.html
Furthermore, if you have an ethernet shield or wifi build in, you could use tcp or udp, to access your arduino from anywhere.
I would always do anything on my own, not using outdated plugins. The learning is much greater and you have simply more control. Since you also need to code your Arduino, you are exposed to writing code anyway.