xfrun4 (belongs to xfce-base/xfce-utils package), which is called using Alt+F2 in XFCE, does not consider user's $PATH to run application. This bug is detailed also here: https://bugs.launchpad.net/ubuntu/+source/xfce4-utils/+bug/306331 Also on this page a patch for this problem is given. I think we can just apply this patch.
Following suit here as per: https://bugzilla.xfce.org/show_bug.cgi?id=6362#c1