I can calm your fear on the last part: I caught Tauros and Miltank with relative little effort. Only thing is, you need to be careful in what part of the route you're using the PokéRadar for them. Sometimes, the southern/eastern part of a route gives other Pokémon than the western/northern one.
As for the Nidoran question: I fear it might be true, since I've had similar experiences.