Starcraft – Do I need the Starcraft 2: Wings of Liberty disk for Heart of the Swarm

Many more units show up in the single player campaign than appear in multiplayer. The following, however, do not appear at all.

Zerg

• Defiler
• Guardian
• Devourer
• old-style queen.
• old-style infested terran.

Terran

• Valkyrie

Protoss

• Reaver
• Dragoon
• Dark Archon
• Corsair
• Arbiter
• Shuttle

If I'm understanding your question properly, in order to have two Heart of the Swarm licenses you need two Wings of Liberty licenses.

Since Heart of the Swarm is not a stand alone expansion, you need to have all the prerequisite games in order to play it (each copy).

You can see for example, on this Cataclysm box art for World of Warcraft, that it requires "Wrath of the Lich King to play". Wotlk says it requires TBC, and TBC requires the base game. It is expansions all the way down. This trend stands true for all Blizzard games to date, as they don't release stand alone expansions.