Andor has never been known for its cameos. However, with part of Season 2 confirmed to be on Yavin IV's rebel base, now would be the best chance to have a cameo for a very specific kind of character.
It has been confirmed in other ancillary materials that Cassian Andor is a Fulcrum agent, which means he's part of a network of spies. From other Star Wars media, we know of other Fulcrum agents that exist in the franchise during the Andor timeline. If we were to see another Fulcrum agent, Season 2 is the time to do it. While there is a chance we will be introduced to a new Fulcrum agent, let's tackle the ones we know about.
Let's rank how likely other Fulcrum agents will show up in Andor
1. Saw Gerrera- Confirmed in Season 2
Saw Gerrera is an interesting case, because he's technically a Fulcrum agent. In The Clone Wars Season 7, Anakin Skywalker had a secret network on subspace communication where people could pass messages. Some people who knew about it were Ahsoka Tano, Obi-Wan Kenobi, and Saw Gerrera. This is the only time that Saw has been associated with the Fulcrum title, so therefore, I count him as a Fulcrum agent. As he's been in all of the Season 2 trailers, he's for sure going to pop up.
2. Agent Kallus- Possibly
Out of all the known Fulcrum agents, Star Wars Rebels' Alexsandr Kallus is the most likely to me. To be clear, I don't think he will be in Andor, because, again, this show has never been big on cameos. However, we know the Imperial-turned-Rebel-Agent was on Yavin IV during the same timeline that Andor will cross into during Season 2. If anyone pops up, it's probably going to be him.
3. Ahsoka Tano- Don't count on it
Though she is the original Fulcrum agent, Ahsoka Tano won't be in Andor Season 2. I'm 99.9% positive about it. This show has never really dealt with anyone or anything with the Force. It's been very Jedi-free. Agent Kallus is a small enough character that he could function like Ruescott Melshi from Rogue One. When Melshi showed up in Season 1, if you knew him, it just enhanced the experience. However, he's just a guy that meets Cassian in the prison arc. Kallus could work the same way as just a guy that Cassian works with.
However, Ahsoka Tano is her own sort of beast. With her own live action series, an appearance from Ahsoka would pull away from Cassian's story. She would steal any kind of scene she was in, outside of maybe a mention of her. Because of this, she won't be in Andor.
Andor Season 2 arrives on April 22 on Disney+.