I added the following to my data acl:
acl_check_content:
  warn    senders        = *@+yahoo_domains
          message        = Yeah, found it

where yahoo_domains is defined as:
domainlist yahoo_domains = yahoo.com.hk : yahoo.com.tw

It matches in the following test where the envelope sender is "tlyons@yahoo.com.tw"

>>> using ACL "acl_check_content"
>>> processing "warn"
>>> check senders = *@+yahoo_domains
>>> yahoo.com.tw in "yahoo.com.hk : yahoo.com.tw"? yes (matched "yahoo.com.tw")
>>> yahoo.com.tw in "+yahoo_domains"? yes (matched "+yahoo_domains")
>>> tlyons@yahoo.com.tw in "*@+yahoo_domains"? yes (matched "*@+yahoo_domains")
>>> warn: condition test succeeded

Repeated the test, and it properly did not match where sender is "tlyons@gmail.com"

>>> using ACL "acl_check_content"
>>> processing "warn"
>>> check senders = *@+yahoo_domains
>>> gmail.com in "yahoo.com.hk : yahoo.com.tw"? no (end of list)
>>> gmail.com in "+yahoo_domains"? no (end of list)
>>> tlyons@gmail.com in "*@+yahoo_domains"? no (end of list)
>>> warn: condition test failed

Using:

senders = *@+yahoo_domains : *@foo.com

it still works:

>>> using ACL "acl_check_content"
>>> processing "warn"
>>> check senders = *@+yahoo_domains : *@foo.com
>>> yahoo.com.tw in "yahoo.com.hk : yahoo.com.tw"? yes (matched "yahoo.com.tw")
>>> yahoo.com.tw in "+yahoo_domains"? yes (matched "+yahoo_domains")
>>> tlyons@yahoo.com.tw in "*@+yahoo_domains : *@foo.com"? yes (matched "*@+yahoo_domains")
>>> warn: condition test succeeded