Welcome to the reflect forum. Normally you do NOT need separate rescue disks. If one system has specialized hardware (RAID drives, etc.) It is best to use that system to create the rescue disk so it has all the correct drivers. If both systems have DIFFERENT specialized hardware, creating a rescue disk that works on both can be trickier. You also should use the latest version of WinPE (version 5) regardless of what the OS is on your two computers. That will make it more likely that your rescue disk will work on both systems.
Of course the only way to be sure is to try the rescue media on each computer. Note that it does NOT matter what OS you are using on the computer(s). The main issue is getting the correct drivers for WinPE IF your system has special hardware.