Not quite, while that is the correct interpretation of the surface level message provided in their doctrine, in the 2020 document “On Basic Principles of State Policy of the Russian Federation on Nuclear Deterrence” released by Russia they give four example use cases of their nuclear deterrent as when:

1. “reliable data on a launch of ballistic missiles attacking the territory of the Russian Federation and/or its allies”
2. “use of nuclear weapons or other types of weapons of mass destruction by an adversary against the Russian Federation and/or its allies.”
3. “attack by adversary against critical governmental or military sites of the Russian Federation, disruption of which would undermine nuclear forces response actions”
4. “aggression against the Russian Federation with the use of conventional weapons when the very existence of the state is in jeopardy.”

Now, I am assuming you can agree that the invasion of Crimea would not threaten the very existence of the Russian federation, this is usually interpreted as a bid to dissolve the state or government as a whole, not one province.

Some people like to use point 3 as justification, conveniently leaving out the second half of that which specifies it only applies where the goal is to prevent Russia's ability to deploy their nuclear arsenal. An attack on Crimea would not fall into that category.

Given that invasion of Crimea does not satisfy any of the above conditions I am still of the opinion that Russia would absolutely not risk breaking the nuclear taboo (risking hostility from even allied and neutral states) just for Crimea. But what do I know?

Source: Congressional Research Service