It seemed like an odd pairing when I first came across it but this will be my second chance to see Eric in person in the last year and though I'd rather see him in a solo appearance, I'll take what I can get.
The US leg of the tour is called the "Remembrance Tour". According to his web-site, McDermott has a strong interest in, and is active in, veterans affairs. His "Rememberance" album includes several of Eric's songs and Eric's fans are well familiar with his interest in WW I. Maybe that's the connection.