I had both the F1229 and his passport copy certified. It was hard enough to get the stupid form filled out correctly (he mistakenly or intentionally did it wrong twice before and drew the process out over a couple months via post. It's a very simple form so one can only assume the latter) and I wasn't taking any chances of immi thinking I forged signatures or something.
I don't believe someone else on here had the form certified for the other parent's signature and they were asked to redo it by the CO because the signature was not precisely on the form as it was in the passport of the other parent. The form didn't say it required certification but clearly if it is certified there should be no question that it was signed by the person on the form in front of a legal witness.