Plants are safe for you but yeast isn’t. It doesn’t mean you have to exclude yeast from your diet entierly but it means you have to be careful.
The main thing you have to watch is the amount you eat. If you eat a very small amount for the vitamins, that’s one thing. But it’s dangerous to use a protein source, a substitute for cheese or something like that.
Some (and possibly all) varieties of yeast have extremely high purine content (it’s nothing like the stuff you were worried about like chickpeas) and have been shown to markedly raise uric acid in humans. So you should assume yeast products to be dangerous unless proven otherwise or consumed in very small amounts. The same goes for any other product made out of single-cell organisms (such as spirulina).
If the yeast is merely killed (which is what I assume “deactivated” means), that wouldn’t help. But yeast could in principle be processed in a way that gets rid of the dangerous part. B12 extracted from yeast is safe for instance.
Now since you are taking allopurinol, you could in principle safely consume otherwise dangerous amounts of yeast. You’d simply have to take enough allopurinol.
The trouble is figuring how much allopurinol would be needed. If you consumed more or less the same amount of yeast every day, it would be straighforward: get a blood test and increase your allopurinol dose if it shows an unsafe uric acid level.
Which is to say that if you had already been taking yeast before your last blood test, the amount you were taking before the test is safe as long as you keep taking the same amount of allopurinol (or more). If you planned on eating a lot more yeast than you used to however, you might need to take more allopurinol.
In my opinion though, you shouldn’t need a drug to make food safe. You never know what effects that would have on your body in the long run. Best eat something else.