Make a software RAID bootable?

Is it possible to create a bootable software RAID0, RAID 5, or JBOD?
The answer is "no". It is impossible to start an operating system off a software RAID0, RAID 5, or JBOD.

A hardware controller is required to be able to to make a RAID bootable. You cannot start an operating system from the software RAID because the RAID is not readable until the operating system is done loading, and the operating system itself is on the RAID.

Your only option is to start an operating system using a software RAID 1. To boot from a "second" drive of a software RAID1, one may need to copy the master boot record first, because typically the master boot record would not be subjected to mirroring.

Complex level RAID100

If you open Wikipedia you find out that RAID100 is considered as nested RAID level. It is said that RAID 100 is a RAID0 built from RAID10 arrays. Thus it turns out that on-disk contents of RAID 100 will be exactly the same as in RAID 10.

So, it is possible to obtain RAID 0 from RAID 100 by removing one of the disks of each mirror set. From the RAID recovery point of view, RAID100 recovery just boils down to RAID0 recovery given that you are able to fetch a full set of RAID0 disks.