The simple answer is yes, but its not the most worthwhile thing to do.
Its not going to speed up rendering time, since the hardware renderer will not make use of sli, it will only use one cards gpu.
If your having problems with slow viewports it will speed those up some, but to me its not enough of a gain to justify the expense.
I just keep viewports optimized, hiding what I don't need to use at the time.
I often display 12M polys in a viewport without issues.