Apologize beforehand that this reply will be a little bit wordy.
I have an AMD RX 480 video card, which is supposedly a few notches above the RX 550 (at least based on their respective prices). I don’t not see a need to install amdgpu pro. The open-sourced amdgpu driver, which is part of the Linux kernel, has been working great.
With the amdgpu, AMD is taking a new route to developing their video driver.
Previously, essentially all the video drivers are proprietary, with an open-sourced version being developed based on hardware specs selectively released by the graphic chip manufacturers, including Intel, NVidia, and AMD.
Now, with the amdgpu, AMD is starting with an open-sourced video driver–thus engaging the resources of the entire kernel developer community at the very initial stage. For those more advanced chips, which would inevitably involve NDA (non-disclosure agreement) with third parties and thus cannot be open sourced, AMD provides proprietary code which is then combined with amdgpu to become the amdgpu pro driver.
Previously, because of the proprietary nature of video drivers, Linux desktop and gaming are always considered secondary citizens to their Windows “mainstream”. I have not tested the amdgpu pro on the RX 480 (don’t see a need to), but on my AMD Carrizo APU laptop, the amdgpu actually outperforms its proprietary brother. Plus, the open-sourced amdgpu will always be a few steps ahead the amdgpu pro. (In other words, the whole process w.r.t video driver developments, open-source vis-a-vis proprietary, is reversed.)
With your RX 550, I really don’t see a need to be bothered with the pro. The Linux kernel in LM 16.04.2 already includes the amdgpu driver.