Yes, they send out resistance. But that's controlled by transistors. And most can't tolerate a higher voltage than the supply voltage on the pot pins (both ends and wiper) because that will mess with transistors controlling it.
And even though the Phoenix looks for a resistance, you can't measure that without voltage. And more likely, it does not really care about the resistance but the pot will just act as a variable voltage divider for the Phoenix in order to set a reference.
So like others said, a digipot isn't a drop in replacement for a real pot.