I love this, both giving and receiving, and we've been doiing it for years with no problems to our health. We do a lot more besides this, but that's a different issue.
You haven't said whether your wife likes you doing this, but if she's open minded, and enjoys a bit of kinky fun, I imagine she loves every minute of feeling you licking and pushing your tongue in as deep as you can.
Regarding health issues, have either of you had any problems so far? I'm assuming not, or I think you would have mentioned it in your question. Many experts theorise that couples who are together for a long time develop a certain level of shared immunity to each others germs; though, as I'm not an expert I don't know whether there's any merit in the research. As I say, we have done this for years without any problems.
I think many couples enjoy this pleasure, you've just got the honesty to ask the question that they are too scared to ask themselves. Is it kinky? Yes, I'd say so, but I love kinky sex anyway. If you enjoy it, why deprive yourself and your wife of a delicious pleasure you can share together.?
I say "Get down and enjoy!!!!!!!"