A "Permanent and Total" rating just means the issues that warrant their 100% rating aren't expected to get better. I know tons of Permanent and Total disabled Vets that would take offense at being called vegetables. Most of them are in better health than I am, and likely better health than the average American their age (they may have tinnitus and gerd and fused vertebrae in their neck/back instead of cardiovascular disease and type II diabetes).
You are probably thinking about Individual Unemployability (IU) which is a higher rating meaning, well, exactly what it says. Still doesn't require being a vegetable.