Are you asking for something above and beyond the contract between you and your photographer? IANAL, but a contract IS a binding legal agreement, and when it comes to law (at least in the US), that should be sufficient. If you are concerned about anything special, you should make sure there are stipulations about them in the contract, such that if anything does go to court, you have a binding legal agreement that both you and the photographer have signed backing you up (and the same would go for the photographer.)
When it comes to general contractors, they are often required by some level of government to BE licensed so they can pursue their trade, as there are often significant safety considerations involved...both for the customer and often for the public at large. I don't believe there is any requirement that a professional photographer be licensed to pursue their trade as I don't think there are many, if any, scenarios where it might pose a safety risk.
I guess I don't understand how liability insurance would apply to wedding photography, unless you are worried they might sue you over damage to their equipment. Again, I would think that is a contractual issue, waiving any responsibility you may have for equipment damage. On the flip side, the photographer may wish to protect themselves from the cost of certain kinds of damage that ARE the direct result of wedding invitees or what-have-you. The two of you would have to agree on where the boundary lies, and both of you are likely going to have to accommodate some level of risk and responsibility there.
These things are generally all a matter of contract, which is the legally binding document that outlines the agreements, liabilities, waivers, and arbitration process between you and the photographer. Use the contract to protect yourself, agree with the photographer about where liabilities lie, how you might arbitrate a dispute, how payment will be handled with (i.e. partial payment up-front, with the bulk of payment due upon receipt of product...which may simply be a set of photographs, or something more complex like a set of photographic prints of a certain quality, a photobook of a certain design, and copies of the RAW images. Insufficient product, incomplete product, etc. could then all be grounds to withhold all or part of the final payment, which should provide incentive to the photographer to produce what they agreed to produce, and not skimp out or produce crappy results, etc.) Once signed by all parties, everyone is bound to conform. ALL participants should be willing to accommodate their part of risk and responsibility in the event that they violate the contract in any way...that includes you, as well as the photographer.