The following lines of plugin_googleotp.py 411 plugin...
# only users in Range
if uid >= 500 and uid < 65534:
otp_users.append(username)
...limit googleotp to user accounts with UID's below the old maximum value (an unsigned 16-bit integer).
Newer kernels use an unsigned 32-bit integer for the UID and GID.
Perhaps we could allow UID values up to the current max (4294967294) to use googleotp out of the box.