Hello lianzx,   It may work but Dell has not validated RHCOS on the R630 or support it.   Maybe someone in the community that has tried it can add their input.   You may verify your install media is bootable and check the system BIOS for which boot mode you need; either UEFI or BIOS.   Your PowerEdge R630 supports these operating systems : [URL]  
I was able to install RHCOS 4.9.0 ISO on a R630 server. But it failed to boot to RHCOS 4.10. ISO. The error is "Boot failed: Please ensure a compatible bootable media is available".  I came across this old post in DELL community: [URL] It mentions "RHCOS isn't supported by PowerEdge yet". I wonder if it is still true. Was it just a fluke that RHCOS 4.9.0 was installed on R630 without issue? Thanks.
Does R630 support rhcos?