If both came up in a game, and a player was able to get both the god who granted a science symbol and the progress token with the same symbol, would that count as having matching science symbols, thus granting the player the choice of an additional green progress token?
Yes. As Califax points out, the last page of the expansion rulebook states that the symbols gained from Nisaba and Ishtar are treated like all others
Could you get both [law scales] and only have 4 other unique science symbols from the cards and claim a victory?
No. Having 2 law scales and 4 other symbols means you have 5 unique symbols. 1 short of scientific victory