Split crown "race" possibly dangerous?
I've never cracked a crown race after assembling many different bikes with different fork/headset configurations. Split crown race makes things far easier and it means one less specialty tool that you need to own or access to get the job done. I've never had an issue with split races either.

As for splitting your own, lots of people do it without issues, if you go this route, I would make sure you gently file the edges to make sure it is deburred with no sharp edges. For how infrequently you need to install/fiddle with a crown race, splitting would however be a last resort for me since you can usually set them with a piece of appropriately sized PVC pipe and a mallet.