Not always, especially with self funded startups. They just don't have the resources/money/manpower to do so.
I've worked with numerous startups for developing their apps and most of them stray away from sending surveys to potential customers. Infact the reliable information for the design specs comes from company's own resources(people in sales, marketing managers, etc).
Exceptions, are VC funded startups, they really have a proclivity towards customer surveys.
About, "How to write personas?"
I am not Jeff Gothelf, and frankly I don't work with startups that provide huge resources to designers. The reality is that for most of the part personas are developed based upon the company's resources, with very little market research done. You will have to do the research all by yourself, you'll have to look into the resources and learn as much as you can from the available resources. As user research is time taking, it is negated because startups are always in a hurry to launch the optimized product as soon as possible.
Ideally, you make a persona from the available resources. And when you start testing your UX, you iterate your persona.
For example, if John's characteristic was "Smart, tech savvy and Fashionable", from testing you may find that John is "Smart, tech savvy but unfashionable". That being said, you are iterating on the user characteristics on the persona, and not on the "type of user". It is important that you get the target user right, otherwise testing in Lean UX would be very frustrating.
With this kind of testing you will understand user frustration, how they want to achieve their targets, etc and can iterate your persona with it.
Again, I would like to remind, persona based UX is the trait of startups (SMBs), majority multi-national corporations are data driven with their decisions.