The answer is a definitive "depends".
It depends if it's a hard poweroff or not. With a hard power off you have a risk that caches didn't get written (with soft- and hardware RAID) and you lose data/files get corrupted. Data loss can occur with both systems.
I've also seen a problem with hardware RAID where the RAID-controller was the issue, it went bonkers and corrupted the data, even a new controller couldn't restore it (thanks for backups though).
In general, I am a BIG fan of Linux software RAID. The reason is you don't depend on one vendor and it has proven its value for many, many years now. It's reliable, you can restore data easily, you can modify it, you can do any thing you want.
In case of a Linux software RAID, when your mainboard etc. fails and you want to put your drives into new hardware you follow these steps:
- Take your harddrives out and put them into the new hardware.
- Done.
How you approach this with a hardware RAID depends on the type of RAID you use. Especially with old hardware this can be a bummer.
Also, always keep in mind:
RAID is not a backup. The main reason for using RAID is reducing downtimes in case of drive fails. And in most cases it avoids having to reinstall and restore from backup but never use it instead of a backup but just as addition.