It's all designed to work together. Powers that "can be used as a melee basic attack" can be used when a Warlord grants you a melee basic, and the same with ranged. If it just says "grants a basic attack" you can use a melee or ranged basic.
Everyone can use a Melee Basic Attack and Ranged Basic Attack: they're just [W]+Str for melee, [W]+Dex for ranged.