Are there any differences that need to be accounted for when changing a hamburger from grilled to griddled?
Does your burger recipe rely on the center of the burger being medium rare?  If so, you may have a problem with the spice ratio because your cooking technique will produce different types of doneness on the grill vs. the griddle.

With the grill you get a higher quantity of crispy burny bits (the Maillard reaction) than you will on a griddle (temperature generally in the high 300s F, as opposed to much higher grill heat).  With the grill at home you can go for a rare to medium rare center. with a lunch truck, you had best go for medium well for safety's sake (and possible legalities). 

The easiest way to know how your recipe will work under griddle conditions is to test it.  Make up your burger, pat it thin and cook it all the way through in a medium heat fry pan (not my favorite way to have a burger, but classic griddle approach).  If all is well, you're done.  If not, well, you've already perfected it once, you'll need to decide what changes need to be made.

But I'm betting that perfection will carry through to the griddle burger just fine.