Fare rule combinations restrictions will likely prohibit combining these fares on one ticket. They may be able to book on two separate tickets on one "itin", but definitely not on one ticket due to the restrictions and agents can't simply override those fare combination rules. ITA Matrix will price out many broken fare combinations if you use advanced controls (for example, using "DL+"), but it won't price out any broken fare combinations that can't be combined on a single ticket. It priced out a broken fare combination through IAH (that was allowed to be combined on one ticket), but it wouldn't show the two fares together that you found as they can only be booked on separate tickets.