I'm not fond of mixing different species of anemones in one tank. However some with larger tanks do get away with having two different ones. For instance a BTA will mostly stay on the rocks, an LTA will stay in the sand bed. there usually isn't anything to fear unless they start to move, and it can happen.
IMO its best to simply avoid the danger of their meeting. There is also fear that a clownfish might swim from one to another thereby spreading the nematocysts. I'm not sure if that can happen anymore, I know I used to know but have forgotten now.
Thomas