I'm able to download and install the stencil directly from my iPad (*) using OmniGraffle-iPad 1.6.1, and the Graffletopia site says that the stencil should work on the iPad. However, I'll host a flat file version of it at
http://bit.ly/AlOHiG for a few days, hope that helps!
(*) Tap the Stencil menu, type the name of the stencil in the search field, tap on the stencil that you want, tap Download button.