I think that the IRS instructions for form 5329 should answer all your questions. Especially pgs 3 and 4 including line 2 where you can remove the 10% penalty if the employer did not classify it correctly.
Line 2 - Exception #1 (ie the rule of 55)
"01 Qualified retirement plan distributions
(doesn’t apply to IRAs) you receive
after separation from service when
the separation from service occurs in
or after the year you reach age 55
(age 50 for qualified public safety
employees)."
Pretty straight-forward to me. No talk about the plan documents having to mention it, but this is commonly brought up as an issue -- in error IMHO.
So, from my perspective, what you are really asking - is a Roth 403(B) a qualified retirement plan?
I have been under the impression that it is, but I will let someone else chase this down.
Here is a link to the instructions for form 5329.
https://www.irs.gov/pub/irs-pdf/i5329.pdf
-gauss