Yes, you could have two or more Global domain documents on one server. However, I don't see who it would help you.
Let's say you have Global domain document with primary domain abc.com and aliases uk.abc.com and eu.abc.com and another Global Domain document with primary domain xyz.com and alias uk.xyz.com. In this case if user has email address:
abc.com - user would be able to receive mail as
[email protected],
[email protected],
[email protected]uk.abc.com - user would be able to receive mail only as uk.abc.com
xyz.com - user would be able to receive mail as xyz.com and uk.xyz.com
uk.xyz.com - user would be able to receive mail only as uk.xyz.com
eu.xyz.com - mail would be rejected.