Will this question be rated relatively high? Or relatively highly?

Solution 1:

These are two different topics:

If sustainability is rated high, this means that lots of new oil fields, power sources etc have been opened up and prospects of blackouts are low. The grammar of the first makes 'rated' a copula and 'high' an adjective. It is the same construction as 'is high' 'seems high' 'is perceived to be high.'

If sustainability is rated highly it means that it is held in high regard. Lots of papers will be published, grants for research funded, medals for progress dished out.
The grammar in this case makes 'rated' an active verb, and those who study the evaluation of these sectors see that there is much activity. The sector is being rated highly.