According to James Hardie's website...you can blind nail with the 1-1/4" roofing nails. They also state that you can nail directly to OSB using 1-1/5" non-corrosive nails at 12" O.C.

Their Installation instructions:http://www.jameshardie.com/pdf/install/install_plank_north.pdf

 

damn it! now i look like an anal jerk!

 

Ya the whole not nailing into studs at butt joints is something that almost has to be ok, mainly because the 2 nails in both pieces only have 1 1/2" of stud to share, meaning you would have to angle you nail into it as if you're too close to the edge you'll blow the corner off. I mark and hit the studs but don't care all that much about joints.

Just use lots of nails, I use the 2" hot dipped galvi and I'm not afraid to use them... When I can't find many studs I add more nails. As Atlantic said Hardie says you can nail through sheeting as long as nails are no more than 12" OC.