I personally would replace all the bleed nipples.  If you had to use moles
grips then a) they were already seized and b) will now be shagged anyway.

I assume you used a proper Ring Spanner first and not an open-ended spanner?

As for bleeding via the pipe/caliper union you can try this but you will
always have a small air pocket in the cylinder.  Being a rear brake then it
might not make that much difference but their is the possibility that over
time the air bubble will migrate back into the braking system.

My advice.  Replace all the nipples and do the job properly.  If you were to
be involved in and accident then insurance companies can be very picky and
certainly will not look favorably on bodged brake systems.

Nick /////