umm.. why not? it's just for zsorting, not for transparency.
plus, there is an alpha-testing mat which doesn't produce smooth edges along the transparent seams, but works anyway, which you should find in the wiki. btw, seems we had this several times ago already...

[edit] k here comes the proof, it works, at least for me:

my mat from the 2nd post, just with the alphablendenable-line commented out:


smooth...

now the alphatesting provided by the wiki...


a bit worse, i think.


both models are one of loopix' free trees, with either material z-sorting probs do not loger occur. just the quality is different.