I don't think its bad. I've never done it myself but you can try using the icer tip...(sp?). Which is a thick and will give you an even line. I believe it's like an inch thick. You can let it crust and smooth it out. HTH! 
I think that buttercream would be find if you feel you have a steady enough hand to do it with the icing tips or the basket weave tips since there are different sizes.
I would use fondant, esp. if you are concerned about bleeding. I once used black buttercream as a "shortcut" around the eyes on faces for a family tree. They looked adorable - until I got up the next morning. 
All my darling little people looked as if they had been beaten during the night - big, black rings around their eyes, and there was nothing I could do about it.
If you use buttercream, cheat a little. Let the "base" buttercream crust or firm up in fridge (depending on your buttercream). Cover the "other than the ribbon" cake with paper - baking parchment or drawing paper, both work well. Make the ribbon as you want, peel off the paper and you have perfect ribbon around your cake.
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