Is it significant that God states that the release of animals was so that they could “be fruitful, and multiply” (Gen 8:17)?

Indeed it is, for such a blessing (or command) was made after the first creation (Gen 1:22,28); to Noah and sons after the Flood (9:1,7); with regard to Ishmael (17:20); to Jacob (35:11); and in other places. On the broader meaning of the phrase, see remarks on 1:22 above.