Some Ghost Heroes can't be picked up. Intentional?

There are eight ghostly heroes.

The below five cannot be picked up (regardless of terrain);

- Clelia the Remembered
- Count Tollan

- Dorn Axegear

- Jen "Bloodfeet" Squishy

- Theobald the Titanic

The below three can be picked up;

- Bolgric "Meteor" Hamsides

- Emperor Uther

- Mahora the Resplendent

I noticed this in the final level of the Under Games, Meat Maker, where the player can find a neutral Theobald.