Hmmmm. Off the top of my head, I'd say no. You could create two recordsets, one for each column of emails. I'd have to go look at UE to see if it let's you use more than one, not sure without looking.
You could also write a single recordset that combines all the email addreses into a single list, or write a query in the database. But that may be a little over complicated.
The only sure way I can think of now is to have two pages with submit buttons, where one sends to the first list, the other send to the second list. That way you're only sending 300 at a time, reducing the risk of server timeouts.