The one Daniel Moore I know of in Washington County had land on lower Antietam Creek, SW of what became Keedysville and not far upstream of Antietam Iron Works. He acquired the land via an agreement of 1754 with Joseph Chapline, when it was still part of Frederick County, but Daniel briefly had owned a tract on Seneca Creek in what is now Montgomery County.
My working theory is that this Daniel (with wife Mary) was the son Daniel named in the will of John Moore, carpenter, of Patuxent Hundred, Prince George's County, MD, whose will was probated in 1754, and is posted here: http://boards.rootsweb.com/surnames.moore/21185/mb.ashx
John had no known son named Zebulon.
A plat of John's land is posted here: http://boards.rootsweb.com/surnames.moore/21184/mb.ashx
Patuxent Hundred did not become part of Frederick County. I think the land was near the raceway.
Daniel of Lower Antietam died testate in 1792, devising to son Richard, daughter Nancy (wife of John Griffith), wife Mary, and conditional land provisions concerning "all my children" (Washington Co. MD Wills A:279-280). This Daniel **may** have had a son Daniel who was living in 1805 but died before his mother did ca. 1812. The latter is presently a rather shadowy figure. The only other known child of Daniel (d. 1792) was daughter Sarah, who married first Samuel Taylor (d. 1786) of what became Shepherdstown District, Jefferson Co., (West) VA, owning land opposite the mouth of Antietam Creek on the Potomac. Sarah mrd. 2d Edward McShane, who operated a ferry from the vicinity of the Taylor land, across the Potomac to the west side of the mouth of Antietam Creek. The McShanes moved to Bourbon Co., KY ca. 1795/1796, and Edward died there ca. Sept. 1796, owning land in what subsequently became the southern edge of Harrison Co., KY.
Daniel is listed during the French and Indian War on an undated roll in Capt. Moses Chapline's Militia Company, while Zebulon is listed on an undated roll in Capt. Joseph Chapline's Militia Company, according to Murtie June Clark's excellent extracts in _Colonial Soldiers of the South, 1732-1774 _.
There were other Moores in this vicinity, and one of the Militia rosters suggests there were at least 3 named John!
I have not run across anything indicating who Zebulon Moore might be related to. Your suspicion about origination in PA is certainly possible. Washington County was a gateway to the West, and there was a lot of inter-County traffic.