Since no one is responding to this, I will.
In short: I don't know if this will cause you any trouble, but if you don't mind taking the drive out of the nas and have the ability to connect to a pc running linux, there's no real harm in trying.
Should you try to update and it fails, you can just rip out
the drive and follow this
guide to reinstall the firmware.
It is always wise to backup the data on the drive, especially before a firmware update, but you can keep the data if you skip the 'format data partition' step.