I believe not.
Because RockBox actually deep sleeps the iPod, so its the same you put the hold button or not.
Actually, its better to put it in hold, so you dont accidentally turn it on and start draining your batteries
Apple OS sleeps the iPod, Rockbox powers it all the way off. Hopefully in the future Rockbox will also be able to sleep the iPod. Because the iPod is fully powered off, it makes no difference where the hold switch is.
Just remember, if you are using the newer iPod bootloader, and power the iPod on with the hold switch in the on position, you will boot AppleOS. If you are using the older bootloader, booting with the hold switch on will clear all your Rockbox settings.