When I used to get ValPak some vendors would use reply cards, so you should ask them to know for sure. I'm sure it is possible. they are essentially a printer and will be happy to offer you a custom piece. [I think]. I used to adv in ValPak years ago but it was a diff product but my recollection is that they are there to make a sale and as long as they can accomodate your needs they will.
I highly doubt they will, I just opened a Valpak today and no reply card inserts, same long double size add slim envelope size paper with just the ad of each company. The only way to do it is have a catchy eye add about insurance coverage that would lead to your website for more info and a toll free number. I am not sure if anybody has done these, but I just went through about 40 of them in the insert and no insurance..that could be bad or good..my guess the insurance companies tried them with no luck, but who knows.