NiMh batteries with Fio

I've got a Fio board, and all the documenation I've found for it mention charging a Lipo battery pack. I've got a bunch of NiMh battery packs laying around, can I just use them instead? Is there something different about the charging circuit that it won't work with a 4-cell NiMh pack?

The chemistries are very different which also means their charge profiles are very different.

The MAX1555 on the Fio is designed only for a LiPo cell.