STM32 Core + NeoPixel question

I am using a few serial ports on STM32F103 - I understand that it provides a hardware buffer.
I also understand that the NeoPixel does stop timers/interrupts while transmitting.

Who knows whatever the serial buffer is affected or not ? (are incoming data still being stored while NeoPixel writes?)

Nothing like that would stop a timer. They are free running, and driven from the clock chain. The UART doesn't have a hardware buffer, but it can use DMA with serial to accomplish the same thing by DMA access to main memory. The bus arbitration for the DMA is complicated, so do you have some links to information about how the STM core uses it? In other words, where did you learn about this?

It might be simpler to just test it, than to dig through all the documentation for that. I think there is a good chance that it might work. Are you already using NeoPixels successfully with this processor? Which library do you use?