Q1: Can I use this card's On Play When Digivolving effect to suspend either my Digimon or my opponent's Digimon?
Yes, either can be suspended.
Q2: At the end of the turn, I used Vortex on this card to attack an opponent's Digimon, this Digimon was deleted in the battle, and I used <Fortitude> to play this card from the trash. At such times, can I again use Vortex to attack?
No, you can't. Vortex on this card triggers at the timing upon the end of the turn. If this card attacks using the triggered Vortex effect, is deleted in battle, and is played using <Fortitude>, the Vortex on this card hasn't triggered after being played, therefore it can't activate.
Lv.5 GrandGalemon ST22-13 SR Ultimate | Data | Bird Dragon/Vortex Warriors/LIBERATOR <Fortitude> <Vortex> [On Play] [When Digivolving] [When Attacking] You may suspend 1 Digimon. Then, this Digimon gets +3000 DP for the turn. --- [When Attacking] [Once Per Turn] If your opponent has no unsuspended Digimon, this Digimon with the [Vortex Warriors] trait may unsuspend.
Lv.5 GrandGalemon ST22-13 SR Ultimate | Data | Bird Dragon/Vortex Warriors/LIBERATOR <Fortitude> <Vortex> [On Play] [When Digivolving] [When Attacking] You may suspend 1 Digimon. Then, this Digimon gets +3000 DP for the turn. --- [When Attacking] [Once Per Turn] If your opponent has no unsuspended Digimon, this Digimon with the [Vortex Warriors] trait may unsuspend.
Lv.5 GrandGalemon ST22-13 SR ultimate | Data | Bird Dragon/Vortex Warriors/LIBERATOR <Fortitude> (When this Digimon with digivolution cards is deleted, play this card without paying the cost) <Vortex> [On Play] [When Digivolving] [When Attacking] You may suspend 1 Digimon. Then, this Digimon gains +3000 DP for the turn. --- [When Attacking] [Once Per Turn] If your opponent has no unsuspended Digimon, this Digimon with the [Vortex Warriors] trait may unsuspend.
Lv.5 グランゲイルモン ST22-13 SR 完全体 | データ種 | 鳥竜型/ヴォルテクスウォリアー/リベレイター ≪不屈≫≪ヴォルテクス≫ 【登場時】【進化時】【アタック時】デジモン1体をレストできる。その後、ターン終了まで、このデジモンをDP+3000。 --- 【アタック時】[ターンに1回]アクティブ状態の相手のデジモンがいないなら、特徴に「ヴォルテクスウォリアー」を持つこのデジモンをアクティブにできる。