Ok to sear beef short ribs from frozen?
Searing frozen meat is fine, and is a useful way to get a good sear without overcooking the inside (since you can sear for longer, and at a lower temperature). There are no food safety issues I can think of which would apply to short ribs but not steaks, particularly since the former are cooked for longer at a higher internal temperature.

The only problem I can think of is if the ribs are frozen into an irregular shape. You want good, broad contact between the surface of the meat and the pan. If the frozen meat only contacts the pan in a few small places, those areas can burn long before the rest of the surface is properly seared. Adding a bit of oil can help with this if the surface is nearly flat. Alternatively, if you have a powerful enough broiler (aka grill), you can use that to sear instead.