For an ethernet connection between 2 points which will be used as point to point communication (for embedded devices). Is internet connection, hubs or switches are really necessary? Or can we still send and receive data from one MCU to another one by using ethernet without using any internet connection, hubs or switches?
There's certainly no need for an Internet connection.
If you want to connect two computers together directly, then you will need to use a crossover cable rather than a patch cable unless the devices you are using support auto MDI-X.
Putting a cheap hub between them will probably be simpler.