Not that I consider that strategy cost-effective in general. For one thing, it's bad PR. (Unless you're some kind of wizard that can spin it like, "we're principled and don't let bullies walk all over us. That's why we hold people to their promises")
Are you hiring a contractor to get work done? Or are you allowing the head of your legal department to pad his resume, while your department is paying for many in house lawyer hours plus (via the contract) many out of house lawyer hours?
Will it reduce the number of incoming contractors? Probably. Will the contractors who'll still chime in be more likely reliable, after considering what they're agreeing with? Very likely.
I doubt it. They're just as likely to be selecting for future contractors who are overly confident / cocky by nature, and/or ones who don't understand how to estimate software projects, and who don't have a good feel/understanding for the risks involved.
Wouldn't it more likely select contractors that have good liability shields and get to charge a premium for working for an asshole company because there are less people willing to do the work? This is how patent trolls are set up with no assets to lose.