Because of the step change in functionality, ChatGPT is not banned. However I am prohibited from using ChatGPT outputs in certain contexts. Unfortunately, Grammarly and ChatGPT are under different application classifications.
The difference is in the value returned. Punching queries into a third party search engine is also risky. If that search engine knew who you worked for, it could extract what you were working on and potentially how competent you were at it.
Now try telling engineers to not use google.
On the flip side, grammarly is often positioned by corporate security as a nice to have feature which can be replaced by offline spellcheck and internal web docs.