I'm building a pair of Orion speakers, and I'd like to use the M200 to drive two Peerless 830452 10" woofers wired in parallel. According to the mfgr data sheets on this driver, it is nominally 8-ohms, so the parallel configuration is nominally 4-ohms. However, some DIY web posts indicate that the parallel combination can dip to 2.5 ohms at some frequencies.

Can I safely use an M200 in this application?

If not, I'll have to purchase another M200 (bringing my total to eight!) to avoid wiring these drivers in parallel.

Outlaw might be able to officially confirm this, but I would not expect a nominal 4 ohm load to pose a problem. It's pretty common for 4 ohm speakers to exhibit regular dips as low as 2.5 ohms.