after the read of his code, it seems that daemon is an systemd OS specific one because it can run with an user different than root without setting a namespace (which is linux specific). Nothing to comment here, it's a dev choice to be not portable.
So forget about running it with uksmd user account.
Now, you are able to run it as root on a terminal but not as a service!?!
try this
[main]
@ type = longrun
@ version = 0.0.1
@ description = "Userspace KSM helper daemon"
@ user = ( root )
@ options = ( log )
[start]
@ execute = ( s6-fghack /usr/bin/uksmd )
Personaly, this kind of daemon will not see the tail of my system :p
