Let's say I'm from Latvia and I get a VOA. Am I eligible for a 7 day extension the same as those who enter on a Visa Exemption?

Actually nobody is granted that - it is 7 days to depart after being refused but in effect no difference except the stamp. Yes you should be able to obtain but might need to show ticket and to obtain VOA expect you will have to show an earlier ticket. If you can obtain a tourist visa prior to arrival I would do so.

The applicant must possess a passport with at least six-month validity and must present full paid ticket which is usable within 15 days since the date of entry