Since BlueOcean change log (https://plugins.jenkins.io/blueocean) highlighted blue-ocean-executor-info:

1.13.1 (March 1st, 2019)

NOTE: blueocean-executor-info is now included in the main blueocean-plugin repository (but not as a required dependency yet)

• ...
• JENKINS-52825 Cannot see executors in Blue Ocean UI

... I gave it a try (v1.13.2 of BlueOcean-Executor-Info Plugin that was kind of merged into BlueOcean-Plugin, I think), but later on found massive log spam in the Jenkins log file:

...
Sandbox » acme.unattendedUpgrade
Sandbox » acme.unattendedUpgrade
Sandbox » acme.unattendedUpgrade
Sandbox/acme.unattendedUpgrade
Sandbox/acme.unattendedUpgrade
Sandbox/acme.unattendedUpgrade
Sandbox » acme.renewCerts
Sandbox/acme.renewCerts
Sandbox » acme.renewCerts
Sandbox/acme.renewCerts
Sandbox » acme.renewCerts
Sandbox/acme.renewCerts
Sandbox » acme.git
Sandbox » acme.git
Sandbox/acme.git
Sandbox/acme.git
Sandbox » acme.git
...

(and I really mean massive).

=> https://github.com/jenkinsci/blueocean-plugin/pull/1931