Got this reply from them a while back when I opened up a ticket. It worked for me.
Thank you for contacting DreamHost support!
I have checked over that error and it seems you are running out of PHP
In order to change the PHP memory_limit variable you will need to create
a custom PHP.ini phprc file by following the steps on the wiki page
Any custom php.ini configurations will need to be done through this phprc
Please use the recommended settings within the wiki and your update
should go through without any issues.
If you need further assistance with this, please let me know and we can
assist you further!