Having a bartender at your next house party? Better read this!
The liability of a host server depends upon the statutes and case law in the state where the homeowner resides. Generally, serving alcohol to minors is the sole basis for liability; while some states hold a host liable for gross negligence or for serving a visibly intoxicated person. Because these parties are not business-related and no exclusion in the homeowners form precludes host liquor liability coverage, the insured would be covered for serving alcoholic beverages to guests, provided the injury is not caused by the use of a motor vehicle. The 2000 (or later) edition of the ISO homeowners policy forms thoroughly closes the door to liability coverage for a loss involving the use of a motor vehicle, regardless of who is operating it. However, coverage for the homeowner would apply to an intoxicated guest who negligently injured someone or damaged property without the use of a motor vehicle.
His bartender friend, however, does not satisfy the definition of an "insured" on the host's policy, so he would not be covered under this policy. Also, the bartender's homeowners policy is likely to exclude this activity because of the business pursuits exclusion. (This activity could be construed as a business pursuit since he is compensated and performs it with some regularity.)
One way to access coverage for the bartender could be to have your client enter into a written contract under which your client agrees to assume the bartender's liability. The contractual liability exclusion of Section II—Exclusions, Coverage E—Personal Liability, makes an exception for a written contract relating to the ownership, maintenance or use of any "insured location," or when the liability of another is assumed by the insured prior to an occurrence. If your client chooses to assume the bartender's liability (not sure why he would do it), the assumption of risk should be limited to that which is covered by the homeowners policy; which, of course, excludes the use of motor vehicles.