Question about AsRock B450M Pro4

You can check directly with Asrock here:
https://www.asrock.com/mb...

It's funny that I couldn't find either RAM in the list. However, the specification states that DDR4 3200 (even with OC) is supported with a Ryzen CPU.

So back to your question, YES you can certainly use both RAM, but the question is whether you can get the full potential of your CPU (e.g. if you want to buy a Ryzen 5 3600 (frequency 3.60 GHz)). Since I couldn't find the max frequency anywhere and it may only run at 3200.

Actually, there shouldn't be too many problems with memory in the board.
However, I would take this memory,
G.Skill Aegis (2x, 8GB, DDR4-3200, DIMM 288)
I have never had any problems with it and it has always been very fast.