A tab control and a layout part are quite different things. You cannot create a layout part inside a tab control, that would be like putting a garage inside a car.
Can you describe what you are attempting to accomplish by doing this? If you do that, we may be able to describe an alternate way to achieve the same result.
I was going to use sub-summaries in 2 different forms, but I suppose I can just use 2 different layouts with button/go to layout scripts to quickly navigate and achieve the same as switching tabs?
Yes and you can even design your layouts to look like two tabs of the same tab control. This is often done when someone wants to use a tab control with a list view showing multiple records inside each tab--which cannot be done except with a portal so they simulate the result with multiple layouts and buttons set up to look like tabs.