1) Pretty much the same thing. However to me multiple filter techniques implies that different parts of the image are printed with different contrast grades. That is the extra effort to use different filters is used specifically with burning and dodging to print different parts of the image with more or less contrast. Split printing to me implies that the image may be all one contrast grade. That is you can still use split printing without burning and dodging to obtain an "in-between" contrast grade. Also split printing to me also implies that the lowest and highest grade filters were probably used. But all in all, it is really basically the same.

2) I used split printing all the time, even on contact sheets. I have found it useful in two ways. First it gives me more freedom when I need to burn and dodge a print - for myself I can generally get a "less manipulated" look to the final print. Second, since I use an analyzer at the easel, the computations come out easier for generating split grade times than to generate grade + time.