The engine won't mind of there's no spinner and the airplane won't mind either.

[The following was apparently my mistake: probably remembering the pointy-nose restriction for contest sailplanes. Sorry 'bout that...] Here in the states, our AMA national organization requires us to use one for the safety of people or things that might get hit by a misbehaving airplane, but unless you've got some regulation like that where you fly, I would think it's up to you.