I'm not related but I'm familiar with Maine.
I'm not sure where you found the reference to a passport in 1898 and a marriage reference to Greenville, Maine as the marriage record is on-line and can be viewed on-line at the Washington State Archives-Digital Archives.
Reference- kingcoarchme 2945
It shows groom:
Nicholas John Stamatiethis - Residence Seattle, King, Washington
Jennie W Erickson - Residence Seattle, King Washington
The Archives give a address at 960 Washington St, Cheney Wa 99004
Phone - 509 235-7500
Perhaps you are aware of this certificate but
This being the case, I don't see how they were also married in Maine.
If John was in Maine, he was always listed as a barbar so prehaps he worked as a barber in Greenville.
I trust this helps.