I'm not gonna debate the finer points of shape changing druids having sex in alternate forms.That road has a lot of pitfalls that can lead to all sorts of nastiness.
Not really. It comes down to two simple logical arguments that would fit both a legal definition and help you to figure out if the event is problematic or actionable.
1. Consent - Are all parties involved able to provide consent? Children and animals cannot consent, but neither is present.
You may be able to make an argument for the squirrel, but the squirrel can leave. Also the illithid tadpole but it can leave also - not to mention it's possibly a unique way to get rid of it.
2. Victimhood - who is the victim here?
In any other logical situation if we go by what people don't like then we become no better than a typical homophobe or racist. If we apply the above standard and there is no conflict then we are in the clear. Our own biases about what is acceptable between two consenting adults are irrelevant. No one is forcing you to experience or partake.