I would advise you to consider do you really have the skills to be a CTO? Have you ever managed a team, had fudiciary responsibilities, engaged professionally in internal and external sales to other executives, lead large technically complex change initiatives? To be fair I wouldn't even consider the following a comprehensive list. If you don't have those experiences now I would advise against trying to learn them at a startup as the support structure rarely is in place and any misstep magnified.

That being the case it doesn't sound like the current CEO is trustworthy or honest with you. If the person they are looking to bring in doesn't have of the aforementioned skills or experience then you should run away now!