My Dh missed the first 2 of mine as he was overseas for work - there were 5 altogether - and wouldn't you know he missed the 2 that were on labour and delivery LOL. Anyway, it didn't seem to matter much. He was able to ask any questions he had at the classes he came to and I got him to read the "role of the birth partner" section in my pregnancy books.
He is really really queezy and hates talking about blood, birth, anything medically related but when it came down to it, he did an awesome job.

It really just depends on how your DH feels about his ability to cope but I don't think it made any difference that my DH missed 2 classes. I did take my Mum to those 2 though - I didn't want to be the only one there without a partner!