Oh geeze. That doesn't even have anything to do with rootless. The issue there is library interposing. Asepsis works by interposing itself into every process that links DesktopServicesPriv.framework and replaces several libc calls.
Good catch on finding something that breaks with SIP, but even if you philosophically disagree with the idea of rootless, you should still agree with the notion that library interposing is a serious security threat and should welcome the changes to block interposing of system processes[1].
[1] From the What's New In El Capitan docs[2], the specific aspect of SIP that applies here is "Code injection and runtime attachments to system binaries are no longer permitted".
[2] https://developer.apple.com/library/prerelease/mac/releaseno...
