If you want to multi-home a X plat machine (configure it to report to multiple management groups) there are a couple of steps you need to take. You can not simple discover it from different management groups as we do with Windows agents.
1. Discover your Linux machine from management group 1
2. Export the certificate from the management server which discovered the Linux box in management group 1. The SCX-agent certificates are signed by a key on the management server that has discovered them, and that machine needs to be a trusted root CA on the management server in management group 2
3. Copy the root CA certificate from the management server in management group 1 to the management server in management group 2
4. Import the certificate as a trusted root CA on the management server in management group 2
5. Run discovery wizard in management group 2 and discover the Linux machine
In this scenario it is very important that both management servers communicate with the Linux machine with the same FQDN.