ucjrd -- it depends on the organization that founded each awards program. I only know the details of how the Tonys work.
For SAG, I know that you are nominated by and voted for by peers. I would imagine there is a nominating committee of SAG members who vote for nominations. Then anyone who is an active SAG member can vote.
Sometimes for an awards show, you do have to submit yourself (or someone who represents you has to submit you). Not sure how it works for the unions' own awards.
"The Spectacle has, indeed, an emotional attraction of its own, but, of all the parts, it is the least artistic, and connected least with the art of poetry. For the power of Tragedy, we may be sure, is felt even apart from representation and actors. Besides, the production of spectacular effects depends more on the art of the stage machinist than on that of the poet."
--Aristotle