the mobo itself can't really be unstable, but yes, if the ram is unstable, superPI will throw an error.. i've found that it's actually more sensitive to ram instability than cpu instability
SuperPI will error for a variety of reasons. If I run my ram 1T at too high an FSB or not enough voltage it will error. However, my system will game playable and 3DMark at a certain cpu voltage and yet not super pi - able. I've found I need another .025v for SuperPi as opposed to running the entire system for everything else.