Okay, something in my init functions for USCI A and B is making them mutually exclusive.
With my current init functions, I can have one or the other working as intended, but not both in tandem.
Oh hell, okay I found it.
The WRST bit when pulled high will actually pull down the Interrupt Enables
Nope, that doesn't seem to be the problem, still getting the issue of either being able to use SPI or UART, but not both (dependent on which init function I call first)