Yeah, that's a great point. No one really knows when an anemone "feels" threatened, so it's impossible to know if/when allelopathy will occur.
I'm glad you ended your post the way you did...it's stuff like this that helps the hobby to move forward, when an aquarist takes a risk, in order to truly be successful i believe (s)he must not only acknowledge the risk involved and try to reduce it as much as possible through husbandry practices, but also do what (s)he can to try to understand the reasoning.