Ive seen this discussion a few times, and no one has had personal experience with increased egg loss, failure to thrives or trainwreck babies from spider x spider. There was one case where a white snake was produced and died but I personally think that was a fluke as its never been reproduced even though breeders do spider x spider pairings every year.

Personally I think the pairing is fine from a health perspective. I believe people only avoid it because most of the time you arent gaining much genetically from pairing a single gene spider to another spider gene animal.