A couple weeks ago I thought he'd sleepwalk to a 55-44 victory, but he came out in support of the immigration ban, and the anti-Trump fervor in the beltway area is very strong.
He's still moderately popular, but if Democrats are serious about it they can win it back. The question is if it's worth it over trying to snatch open seats in Michigan, Nevada, Florida, etc. or trying to oust Scott Walker. I think he's still favored to get reelected just because Dems have so many other races to focus on.
Depending on the national mood, Democrats might not need to invest all that much into the Maryland race at all. Simply because of its heavily Democratic political composition and anti-Trump attitude, Hogan might be overtaken even by a generic Democrat if the Trump backlash grows large enough. Maryland will obviously be one of the most intense focal points if such a development were to occur.
I agree though that it's not the most imperative governor race, Maryland won't be swinging towards the Republicans anytime soon on either the federal or state level and Hogan tends not to rock the boat that much. Hogan very well could end up sinking himself though if he continues to issue unwise declarations of support for Trump's actions.