BUDS drop out rate is about 92%, and another 1-2% pass BUDS, but don't make the teams, for whatever reasons....so that's about a 5% chance of success.
He was projected to be a day 3 draft pick..which means rounds 4-7..and stats say that players drafted then have about 10% chance of becoming a starter..
However, man more will make a team, either via the draft, or undrafted signee. Some of these will last a few seasons, but many are cut during training camp, or in their first season. Once becoming a SEAL, they stay for many years...
Just read an interesting book about life as a marginal player in the NFL
It's very credible because I can compare it to my buddy's kid who spent 5 yrs in the NFL with 7 different teams.