Warming up soup in crockpot
Short answer: yes - the crockpot will heat it sufficiently. 

You might find it easier to transport in a sealed container and just use the crockpot to heat/maintain temperature at the party.

However, the time taken for a crockpot to heat up is substantial compared to using a stove-top pan or even a microwave. Crockpots are really designed to slow cook foods, and maintain temperatures for keeping foods warm.