Ok, turns out the real answer is that xflock4 (which is what xfce uses) is just a script that tries, in order, gnome-screensaver, xcreensaver, xlock.
Since siduction is using lightdm with their xfce iso, it's possible to lock the screen using it instead.
Create a new file in /usr/local/bin called xflock4 and just paste in some super simple code:
#!/bin/sh
dm-tool lock
exit 1
make it executable
$ chmod a+x /usr/local/bin/xflock4
and off you go. Note that dm-tool lock is the lightdm command to lock the screen. This might not be as secure as using xcreensaver but it's fine for my purposes.