Ant = Ari
Fang = ga
And = to
You = U
It's a pun on arigatou.
It was a fun theory. But in truth, IN was the only one that says "ant, fang and you". In EoSD it looks like this:
Special Thanks
ant
fang
and All Test Players
and you...
In PCB:
Special Thanks
ant
fang
pbg
and all test player
and you...
Now consider the following:
-The names "ant" and "fang" appeared in the games from EoSD (2002) to IN (development period from 2003 to 2004).
-In PoFV (2005), "ant" and "fang" disappeared from the Special Thanks section, replaced by four playtesters.
-Starting from MoF (2007), the only name in the Special Thanks section has been his girlfriend and later wife, Ki-san.
-These two people are neither part of the Seihou crew (like Ponchi/pbg is) nor on the list of his doujin friends (e.g. the folks who made Uwabami Breakers).
-After graduation in 1999, ZUN had been living in Taito's Ebina dormitory. His dormitory address was actually written as contact info
in the game manuals.
-He moved out of the dormitory at the end of 2004 (source:
ZUN's diary).
冬コミ前だ というのに引っ越しももうすぐ行います。しばらく不通になってしまうかも。
The Winter Comiket is near, however I will have to move soon. You might be unable be to contact me for a while.
It's quite reasonable to assume that ant and fang were his roommates/colleagues from the Taito dormitory, who helped playtest EoSD, PCB and IN. It'd be natural for them to never show up again afterwards.