Analogous to bug #142604 and bug #143660 sys-apps/hal-0.5.7.1 should not depend on sys-apps/hotplug.
The reason is that hotplug and udev conflicts with each other because of udev's built in hotplug functionality. So hotplug and udev shouldn't be installed parallel.
I've explained the reasons for this more detailed in the bug reports mentioned above.
It would be better if hal depended on sys-apps/hotplug-base because this is a dependency of hotplug as well as of udev.
*** Bug 145806 has been marked as a duplicate of this bug. ***
Actually yes it should. According to the udev author himself, udev does not provide that functionality fully yet.