In Pokémon Unite, Physical and Special is split between Pokémon. So an Attacker uses Attack for damage, and a Special Attacker uses Special Attack for damage. Therefore, using the Special Attack Stat. However, for most Special Attacker's, their basic attacks deal Physical damage (Atk), with their moves and boosted attacks dealing special damage. There are some exceptions to this, including:
- Gengar
- Armarouge
- Alcremie
- Alolan Raichu
- Inteleon
- Mewtwo X
- Miraidon
- Galarian Rapidash
For Physical attackers, like Tyranitar, all of its moves are Physical, even its normally Special move, Dark Pulse and Ancient power. Its power is based on its Attack stat, so it only gets bonuses from attack boosting emblems or items.
So basically, the answer is yes there is a SpA and Atk it is between Pokémon. While some Special Attackers use Attack for their basic attacks, all their other moves - and most of their damage - come from Special Attack.
Source: Experience and UniteDB