I'm not sure I understand your question.
If the question is: "I'm developing a product page, but I don't have a product yet. Should I use personas to drive the product page design?"
Then my answer would be absolutely. Even if you don't have a product, you should design your product and web site in order to captivate and address the questions of the customers you are trying to target.
You could argue that you want to develop a web page that is just for the purpose of creating lead generation, so the page could have a generic message and asks people for their emails.
But wouldn't it be more effective if you designed the page in a way that I understand what you are building and made me interest in it? I think it would increase the likelihood of me giving you my information.
Personas allow you to focus on the customer segment you are targeting. Every decision should be made taking your customers into consideration (even if you are still trying to get customers).
Instead of thinking about the customer that might buy your product, it helps to think about Suzzy that is a mother of 3 and would really be glad if she found that the product you're building is available at her favorite retail store.