Technically, no. This is actually a quite common combination around here, spaying does isn't that much of a dogma outside the english speaking part of the world. But spaying the doe does have advantages, espacially if you plan to house them indoors. There are also health benefits that outweight the risks for a lot of people, not to speak of mood swings and false pregnancies. Then there is no risk of pregnancy - one of my does got knocked up by a wild buck (not likely in the US, but possible over here) and last year I found a neighbours pet buck inside my fenced hutch area - twice.
It really depends on the individual characters how well they get along, hormonal behaviour can interfere with bonding, and put some stress on the relationship, like if the doe is dominant, but mixed couples are the most easy ones.
If you don't spay the doe you'll need to keep the buck seperated for at least 4 weeks, they can be fertile that long aftere neutering.
I did let my free range house rabbits together as soon as the doe was healed up after a few days, didn't see any reason to wait. My buck is still intact though. It's something different if trying to bond two neutered bucks, then I would wait the 2 months for all hormones to dissipate.
I have two pairs of intact does, if they characters match (a more sensitive issue in this combination) that works too, although I skipped the bonding stuff by keeping daughters that got along well with the mum. It's not like they only become social animals through spaying/neutering.