Interesting question! I don’t think that Venus’ atmosphere would be friendly to humans or plants. One major difference between the atmospheres of Venus and Earth is that Venus’ atmosphere is made up mostly of carbon dioxide (CO₂), while Earth’s is made up mostly of nitrogen (N₂). Plants use CO₂ from the atmosphere to grow and store energy, but just because Venus has more CO₂ than Earth doesn’t mean that it would be a good place for plants to live. Another important part of photosynthesis (how plants use CO₂ to grow and store energy) is sunlight. Sunlight provides the energy that drives the chemical reactions of photosynthesis. Venus has a very dense atmosphere (the pressure on the surface is about 90 times greater than at the surface of Earth; (Hamblin & Christiansen, 2004), and I think this would probably block a lot of the visible light that plants use in photosynthesis.

CO₂ is a greenhouse gas, meaning that it traps energy from sunlight and makes the planet hot, so the surface temperature of Venus is almost 500°C (Hamblin & Christiansen, 2004). That’s really hot! Also, Venus has very little water and a lot of sulfuric acid in its atmosphere. Because the atmosphere of Venus is dense, hot, and acidic, I don’t think that plants would be “happy” there. Of course, neither would humans.

reference
Hamblin, W.K. & Christiansen, E.H. (2004). Earth’s Dynamic Systems. New Jersey: Pearson Education, Inc.

The atmosphere of Venus contains lots of carbon dioxide, which is what plants use to make food and "breathe." So plants would like it more than we would. Still, the temperatures are around 800 degrees F, the pressure is nearly a hundred times that of Earth, and it rains acid. So really plants wouldn't even like that atmosphere as a place to live. It is even hard to land probes on since it is such a violent place.

It's not. The atmosphere of Venus would kill any living thing, plant or animal, from Earth that tried to live there.

Most of the atmosphere of Venus is carbon dioxide, which plants could use for photosynthesis if the rest of the atmosphere were more habitable or there weren't too much carbon dioxide, but that much carbon dioxide and no oxygen is toxic to plants.

The thickness of the Venusian atmosphere is also why Venus is so hot; it's the greenhouse effect, but so powerful as to make the planet unliveable, unlike Earth which might become merely uncomfortable with global warming.