methyl - I have not seen a POSIX specification for finger stating that it reads any given file. However, it does read other accounting files. See above. On Solaris, finger reads /var/adm/utmpx. Read the man page.
Gogol - It looks like wtmp is being updated. last should work as methyl indicated but without the -R. There are also wtmpx entries on your system. wtmp is written to only if the file exists, and for you is not part of the picture for finger.
what does
ls -l /var/adm/utmp
show?
if you grep for your username in umtpx what do you get? -- if it works you will see a lot of garbage characters. If they trash the screen use the reset command.
finger is ready to try to match stuff in the gecos field and it marches to its own beat with respect to user names. You have concealed the user's real name and that is probably what is wrong. Is the is user name a mix of 8 characters or less of all lower case letters or digits?