The reason I ask this question is because I have found about 20 designers who have potential to work on my project, and would like to contact them. Should I send them a survey to get an idea about their interest before I start email conversation with them?<p>Thanks for your feedback!
Good UX and UI designers require a period of acclimation to a certain industry. Be prepared to educate them so that they can best optimize for your product domain. It's unlikely that you will find many within specific niches, so you will definitely go through a period of education.
I found a designer on Dribbble by just emailing them with a brief explanation of what I need, what my budget was and asked if they were interested. Make sure you only ask people who's work you actually like and you shouldn't have any problems.