Sorry to be the one to disagree... while the RSM has T5 lighting they are not HO nor are they individually reflected. Therefore they are no more intense than std PC's. Actually, PC's have more light output than T5's in general. But thats another subject...
While a bta may survive under these lights IMO/E its not the healthiest environment for it, the lighting is marginal (dispite what the animal looks like) and should it move to the lower half of your tank the situation may worsen.
Also if an anemone dies it most certainly will skunk your tank, esp an anemone of any size mixed with a tank this size. Not many things in your tank will eat it, they decay very very quickly and they have the same effect as a dead fish does. If the anemone was tiny say a 2" give or take then no the effects wouldnt be bad but 4+" anemone... it would be best to remove it asap if it dies.
The success with these animals should be measured in years not months or weeks... Again this is something that is on that grey line with lighting, I personally would not reccomend it although Im sure its done. I would be anxious to hear of success with one like the RSM and an anemone for 2+ yrs without it splitting. That would be considered success IMO.