Honestly so long as you don’t go into the bars on Alien Night (if you have Get Together) your chance of actually running into an alien in the wild if you’re not playing the Science Career is pretty slim. I’ve only come across one hidden alien in my time of playing the game and that was years ago. And the only non-science career abductions I’ve had is after my sims have gotten into a relationship with an alien and/or had a baby with them. It varies for everyone but I think the chance is pretty remote these days. They’re definitely not as intrusive as Vamps unless you go to the bar night and have the game spawn a bunch of them. Once they’re spawned from alien night they wander around neighborhoods and show up on lots like any townie in the pool. Though if it happens you can go into Manage Sims and delete them.
As for the Science career it’s def harder to avoid them if you have a sim in the career because it’s designed around them. You can use the dish to stop abductions but unless you’re using a mod to stop them from spawning at all you’re going to get a few of them to spawn for the career.