The literal answer to this question is no, you do not need Gmail. However, you do need a Google Account. You can create a Google Account with any email address, not just Gmail. There are a variety of tutorials on the internet which you can search for, but the easiest way is to just start with this link:
If what you really want to know is "Can I use OrbitKit without Google?" then I'm afraid the answer is no. Instead of building a username/password system (with all the risks and liabilities), we decided to offload that work to a trusted third party. It has allowed us to focus on building productivity features instead.