My DD is completely unvaxed and currently attends a licensed co-op preschool in Alberta. There was a question on the form "is your child up to date on immunizations?" and I just checked off no.
I think it's just one of those bureaucratic annoyances...I think if Big Brother really wanted to get at us, it's more likely through the databases maintained by the local health nurses than by the forms the preschool keeps on file. The local nurses can see that I've never brought my kids in for vaxes.
And as for excluding the unvaxed kids when sick, I think it's more at the teacher's discretion. Ours is pretty laid back...sniffles OK, but no fevers and coughs etc. And our teacher says sick kids stay home, vaxed or not...as for whether or not she'd keep my healthy DD home if there was an outbreak of WC or something, I don't know, but that's always a possibility with any school.