It would, I feel, in the end come down to the judgement call of the host of the alt slam.
it's their event and they are overseeing the theme.
I personally would allow non labour poems(although strongly encouraging themed work)in the open mic,but once the labour slam itself was underway I'd dock poets points or DQ them for not following the underlying rule which is that work must be labour related.
were I running the nerd slam i might even go the route that shappy does-were you must win head to head nerd trivia to compete.
ones nerd cred must be solid.