Can I just disable updatedb?

Yes you can disable it in the crons or remove the package that provides updatedb. On a Red Hat system you'd go about the steps in determining if anything requires it prior to removal.

1. First find out where the program is located on disk.

   $ type updatedb
   updatedb is /usr/bin/updatedb
   

2. Next find out what package provides updatedb.

   $ rpm -qf /usr/bin/updatedb
   mlocate-0.26-3.fc19.x86_64
   

3. See if anything requires mlocate.

   $ rpm -q --whatrequires mlocate
   no package requires mlocate
   

4. Nothing requires it so you can remove the package.

   $ yum remove mlocate
   

You can disable the scanning of directories that has many files (/var/www for example) by editing the /etc/updatedb.conf configuration file. If you really want to disable it, then just remove the cronjob.

Remove it using your package manager, if another package uses it, you will know, since it has to depend on it (package dependency).

I have a server with Nginx, php-fpm and mysql, and it works beautifully without updatedb.