It's a bit difficult to measure whether he is still a viable bull, as you say he has no results to prove it since Daizy's birth back in 2009. When his brother was back on site, it's possible that only Samson was given the opportunity to breed with Rozie (both of them couldn't have been in with her at the same time). Perhaps he was preferred over Albert for some reason or another. Cows cycle over a period of a few days too, so it's also possible both bulls had the chance and Samson just prevailed, maybe having access to her first.
This time around, AI would have surely been done first as soon as her cycle began, with Albert given the chance afterwards. If the AI procedure somehow didn't work (which is unlikely), he would've acted as a back up but in the case the procedure was successful (as it was this time around), he wouldn't have been able to impregnate her!
On Albert, he does still have TB so is spending all of his time by himself from what I've heard.
On the topic of potential bulls, there isn't that many bulls available. The only ones I can think of are Johnson (at Columbus) and Raja (soon to be at Columbus). The only issue here is Albert would need to be sent elsewhere for a new bull to be acquired and this would be very difficult with Albert's current health status.