The lien waiver is a good tool for the owner, but I think it's disingenuous to require a lien waiver from a sub prior to the job starting, or prior to getting paid. That's basically telling a sub "dude, you're not getting paid." It's supposed to be an item to be executed at time of final payment. An "ok here's the final check, sign the lien waiver and we're done" type of deal. You state in the contract that final payment will hinge on signing an unconditional lien waiver, and that any subs your GC hires will be subject to the same contract terms, and you make sure you have a written list of subs and all their insurance certs, and they know in writing that they're subject to the same terms as the GC.
But you'd be surprised how that tool gets used.
I dealt with a big construction management firm (well known to anyone in the business) a few years back on a plant expansion. Humongous multimillion dollar job. Our work had just been granted substantial completion, so we were due the final payment from the schedule of values, less the retainage, which would be released at the time of commissioning according to our contract. The CM firm sent us a letter stating we had to sign a lien waiver prior to receiving that final lump. That was just crazy. We said no way, and pay us according to the terms of the contract we all agreed to. We'll sign a lien waiver after we get paid the retainage. We got paid the final lump (2 months late), but they forgot about the lien waiver and hung on to the retainage even after the plant went on line. We had to call the plant owner, and we found out the CM had been paid everything already, but had complained to him that they didn't make enough money and had been looking for extras. We hadn't submitted a single change order, and we asked the owner to call the CM, because according to our records, we still hadn't signed a lien waiver and we were considering executing a lien on his property (we had only a handful of days left where we could). We got paid by the CM within 10 days.
So in that case, the CM tried to use the lien waiver on us as his fall back: in case he didn't make enough money, he wouldn't have to pay. In the end, we used the unsigned lien waiver to demand payment.
Bottom line, this guy you have isn't insured to do the work. If you ANY trouble putting a scope or a contract together, or need help evaluating something, contact me. I don't come to Nathan's site to sell anything, so understand that this an offer of help. I'm in NJ, and I've been around the block.