Technically SUM could and was tried running under WinPE. However we have not performed any extensive testing on it under WinPE environment. One of the key points about SUM - is that it is used to capture user personal data, however under WinPE there is no personal data apart from perhaps user files that cannot be captured (for whatever reasons) under main OS.
Maybe what you are after is for the SUM to capture personal data from another mounted volume under WinPE (other than x:)?