i think it's reasonable for any investor putting personal money into a new venture - which is the ethos of the programme - is entitled to make some pretty deep enquiries about the prospects for the venture.
As I understand it, the Dragons are bringing their individual expertise as well as financial backing, which is far more important - and if they are going to spend time with a new partner, they need to know what they are getting into, and if the project has a reasonable chance of success.
if i was a Dragon asking questions and getting vague or 'don't know' answers, it would colour my willingness to put my money and time into a potential project.
So i think it's reasonable for someone to ask about prospects and success thus far - even if there is no sales and no track record, the Dragons may still stump up of they see a genuine potential prospect in front of them.