Yes, you can do POST request types with RedLine. To do this, you will need to add your own Custom Test Script.

You can find information and examples at https://www.redline13.com/blog/writing-a-custom-load-test/.

If you download the first example file at the bottom, it will give you the basics of what you will need.  The main thing you will change is to add an array of POST variables as the second argument to goToUrl.

If you need any help, please let us know.