Hi Jay,
Yes, many of Yahoo's IP addresses are listed on SORBS. That's not going to get fixed.
The best you can do is try to convince the person you are trying to email that them or their email service, whoever is responsible for the incoming mail servers, to stop using SORBS as an RBL.
Personally I think using SORBS is OK as part of an overall spam score (for example,
using SORBS within SpamAssassin), but not as an RBL configured as a strict allow / reject decision making mechanism.
The only RBL's I trust as strict accept & reject decision making are
Spamhaus and
Invaluement.
Please feel free to send the link to this discussion to the person you're trying to reach or their mail support if they'd like to discuss with others that run mail servers.