Can confirm what Machiel tested as this is what is happening on my SMP server. Low spawn rates are directly affected by render/view distance. A view distance of 10 on my SMP server and spawn rates are normal but the server lags like crazy/tick is through the roof. If I set it to 9, it's a compromise between lag and spawn rates. If I set it to 8 lag/tick virtually disappears... and so do hostile mobs.
Can confirm what Machiel tested as this is what is happening on my SMP server. Low spawn rates are directly affected by render/view distance. A view distance of 10 on my SMP server and spawn rates are normal but the server lags like crazy/tick is through the roof. If I set it to 9, it's a compromise between lag and spawn rates. If I set it to 8 lag/tick virtually disappears... and so do hostile mobs.