The main difference between an escort and a domme is that an escort will sleep with you.
Seriously, an escort is someone who gives her clients sexual satisfaction for a price. With an escort you, the client, are in complete control. What you say goes; what she wants is irrelevant or at least secondary. If you want a blow job, the escort will provide it for you, whether or not she's attracted to you or likes giving blow jobs. She will do what you ask in order to earn a fee. Now, you can ask an escort to urinate on you or beat you with a belt, but that doesn't turn her into a domme. She may be