Funny, I was thinking of writing up my own selection of things to allow Blood Raven marines in Deathwatch. Seems like you guys beat me to it, but there's one thing that's missing, and that's a chance to choose what Past Experience you endured before entering the Deathwatch. So I came up with the following:
Blood Ravens Past Events - Roll a 1d5 and consult below.
1. The Purging of Cyrene - You were part of the Company that accompanied Captain Gabriel Angelos to Cyrene for the Blood Trials. But something occured on the planet that lead to the Inquisition declaring Exterminatus upon the world, leaving it a blasted world devoid of life. What lead to the Exterminatus has been classified to the highest degree, and you have sworn never to reveal what transpired.
2. The Fall of Tartarus - You fought on the world of Tartarus under the command of Captain Gabriel Angelos against Orks, Eldar of the Biel-Tan Craftworld and Chaos Space Marines of the Alpha Legion. Though Tartarus was lost to a warp storm, you managed to escape with Gabriel Angelos along with many of your Blood Raven brothers.
3. The Kronus Campaign - You fought on the world of Kronus under the command of Captain Davian Thule against a multitude of foes, including Orks, Eldar, Tau, Necrons, Chaos and even the Imperial Guard loyal to the Imperium (though that incident has been covered up from the rest of the galaxy). Under Davian Thule's command, you and your brothers managed to seize victory and crushed all opposition, claiming Kronus for the Imperium.
4. The Kaurava Campaign - You fought in the system of Kaurava under the command of Captain Indrick Boreale against a multitude of foes, including Orks, Eldar, Tau, Necrons, Chaos, Dark Eldar and even the Sisters of Battle and the Imperial Guard (though those incidents have been covered up from the rest of the galaxy). Though the campaign was a dismal failure that cost the lives of many Blood Ravens, including Captain Boreale himself, you were among the few who managed to survive and return to the Chapter.
5. The Aurelian Campaign - You fought in the sub-sector Aurelia under the command of Force Commander Aramus against the forces of Orks, Eldar of the Ulthwe Craftworld and a splinter fleet of Tyranids that was once part of Hive Fleet Behemoth. Though the Blood Ravens were few and your enemies many, you managed drive back the forces of Orks and Eldar and destroyed the Tyranid Hive Fleet with the aid of Captain Gabriel Angelos at the final moments.
I purposely did not include the Second Aurelian Campaign. Think about it. If you played through as Pure (which I did) and found out what you did during that campaign, you'd probably want to focus on that and not join the Deathwatch. If you played anything else, the Deathwatch would probably not want a Space Marine already corrupted by Chaos, no matter how slight it may have been, to join their ranks.