I have tried booting FreeBSD, which should have SMP support per default, and it also fails to find more than one CPU. And this particular server is even listed here:
http://www.bnv-bamberg.de/home/ba3294/smp/rbuild/ as successfully booting FreeBSD. Switching the CPUs around hangs the machine, so all this leads me to believe that it is the fault of the hardware, not OpenBSD. Too bad, well, I guess I will have to make do with a single CPU... Thanks anyway.
