same material from both tape formats?
 

I have some worn out beta tapes that I'm thinking of replacing with the tape spool from new VHS blank tapes since blank betas are hard to find these days. My question is are the tape ribbons made of the same material and size (1/2")?

Beta is 1/2" while VHS is almost exactly 1/2" (it's really 12.65mm). They should fit.

Why don't you just stock up on some new blank beta tapes:

http://www.high-techproductions.com/betamax.asp

I've wondered for a while if there was any market for copies of new movies on Beta format, done with permission of the studios of course...
I would prefer to buy new releases on CED however ;)