one of the OS_ properties on the server should tell the architecture. x64, x86
OS_PLATFORM is the property. If you install the 32 bit agent on a 64 bit server, it will not show x86_64 though. The 64 bit agent will (at least on 7.4.2). When you do a patch analysis job, the job will determine which patches apply for that server, you don't have to do anything different if its 64 bit or 32 bit. 64 bit patches will show up if the server is 64 bit.