Are the wordpress settings (abspath, disable core updates) added by SiteGround of any use after I’ve migrated to a different host?

Both of these settings are used in all WordPress installs – they’re not specific to any host.

The ABSPATH ensures that WordPress knows which folder to look in to find all of its files.

Whether Core auto-updates are good or bad really comes down to your own processes and preferences. For security reasons, enabling the updates is recommended. However, if you are running a site with a lot of plugins and/or themes where small changes to Core may have major affects across your site, you may want to instead build a staging/dev site which is a copy of your live site, but where you update everything and test the effects before updating your live site. WordPress Core developers try not to break things in changes, but particularly with the Block Editor some things like block classes and styling may vary from version to version, so if you’re doing for example a lot of custom blocks and modifying Core blocks, you might be better off not enabling updates on your production site.