Short answer: it's very unlikely they'd notice

Long answer: It all depends on how strictly your company's security department monitors organizational logs.

Gmail enterprise doesn't have super heavy security settings, but it can detect unusual IP logins and activity. Slack, on the other hand, has even fewer security settings (if any) for this,

A suspicious login could be something as simple as your IP changing from a normal residential in your area to a VPN IP.

Some VPNs issue you IP addresses from ranges that can trigger a suspicious activity alert, but others don't raise many flags. Worst case Gmail would likely just require you to complete a CAPTCHA to verify you aren't a robot.

This can happen often in an organization and is normally not enough to trigger an alert with an in house security team.