well, i don't know the temp of steam, but it is hot enough to burn skin easily.. i would be concerned it may damage the thc.. if it wouldn't damage it due to heat, i would think adding moisture like that would greatly increase your chances of mold/bud rot...
i can not think of anything positive that would come out of steaming a plant.. again, think extreme heat.. the plant doesn't like the temps raising above 100 degrees (water boils at 212 degrees so the steam would have to be AT LEAST that hot.. probably hotter)... doubt it would enjoy being steamed.. lol