Yes, these are done online now all the time. The vast majority of producers that raise breeding bulls or registered seed stock broadcast the sale in real time on the internet and have options for online bidding, and have been doing this for quite awhile.
Producers can also sell large groups of calves online through video marketing. Superior Livestock started video marketing cattle in the late 1980's and transitioned it to the web. Great option to sell directly off the farm without having to take calves through a sale barn, reducing the transfer of infectious disease and also saving the producer from paying yardage and some commission from the sale.
My dad is 68 and has bought a dozen bulls online; watches a lot of sales during the winter without buying as well. 10 years ago I would've described him as technologically inept and I'm still a little amazed he can pull this off.