I die of pain for one evening and come back to you all talking about rimming! I reckon rimming is alright Lyra. Maybe chuck it under the same risk level as a glass of wine?
There's obviously some bacteria but if it's cleaned and you go brush and gargle after rather than sitting there with arse mouth I reckon it's clean enough to really minimise any risk.
If you're really nervous about it, you could ask the midwife and then come back here to tell us of your embarrassment. 