All my cacao are from seed. My son just purchased a farm in Belize and they planted all theirs from seed. We have a Swedish friend with a cacao farm in Fiji, and they not only plant all theirs from seed, they sow them directly in the field, skipping pots altogether.
So yes, they will grow true to seed. The caveat being that they are self-incompatible, so if you only have two trees, one forastero and one trinatario for example, the offspring will be a cross between the two.
Cheers,
Carolyn