Yes, it is. In this case, even if <De-Digivolve> de-digivolves an opponent's Digimon into a Digi-Egg card without DP, it won't be trashed until this card's [On Play] [When Digivolving] effect is resolved, so that card is still treated as a Digimon. Therefore, this effect's "if your opponent has 2 or more Digimon" condition is still met, and you can return 1 of your opponent's level 4 or lower Digimon to the hand. After returning it, the Digi-Egg card is trashed. In addition, if a Digi-Egg card is returned to the hand by this effect, that card is placed at the bottom of the Digi-Egg deck.

No, it isn't met. In this case, if <De-Digivolve> is used to de-digivolve an opponent's Digimon into a Tamer, the "if your opponent has 2 or more Digimon" condition in this effect is no longer met.

It can play 1 [Blue Flare] trait Digimon card with a play cost of 5 or less, or it can play 1 [Xros Heart] trait Digimon card with a play cost of 5 or less.