So, the problem is solved. First off, its SUBSYSTEM is input not usb. We're handling a evdev device creation, don't forget. The final version:

ACTION=="add", SUBSYSTEM=="input", KERNEL=="event*", GOTO="wacom_rules"
GOTO="wacom_rules_end"
LABEL="wacom_rules"

ATTRS{idVendor}=="056a", SYMLINK+="input/wacom"
ATTRS{idVendor}=="056a", ATTRS{idProduct}=="0000", SYMLINK+="input/wacom-tablets/penpartner input/wacom-tablets/penpartner-%b"
ATTRS{idVendor}=="056a", ATTRS{idProduct}=="0010", SYMLINK+="input/wacom-tablets/graphire input/wacom-tablets/graphire-%b"
(...)
ATTRS{idVendor}=="056a", ATTRS{idProduct}=="0047", SYMLINK+="input/wacom-tablets/intuos2-6x8a input/wacom-tablets/intuos2-6x8a-%b"

LABEL="wacom_rules_end"

ATTRS looks for the file on the parent directories as well, solving the problem here.
One note is that if you try to get ATTRS{idVendor}=="056a" on the first rule to avoid repeating on all rules, it won't work, no idea why udev behaves this way.