Does the family have the option?
Pretty sure that's the case. After all, the piece of land doesn't matter compared to who they were and what they did. Any vet can be buried there, but families don't necessarily want to drive a thousand miles to visit their grandfather's grave.
ETA: www.arlingtoncemetery.org/ might be the place to find the official rules, but I can't get anything from there to load in my browser.
ETAA: I can't spell.
Eligibility for Interment (Ground Burial)
The persons specified below are eligible for ground burial in Arlington National Cemetery. The last period of active duty of former members of the Armed Forces must have ended honorably. Interment may be casketed or cremated remains.
Any active duty member of the Armed Forces (except those members serving on active duty for training only).
Any veteran who is retired from active military service with the Armed Forces.
Any veteran who is retired from the Reserves is eligible upon reaching age 60 and drawing retired pay; and who served a period of active duty (other than for training).
Any former member of the Armed Forces separated honorably prior to October 1, 1949 for medical reasons and who was rated at 30% or greater disabled effective on the day of discharge.
Any former member of the Armed Forces who has been awarded one of the following decorations:
Medal of Honor
Distinguished Service Cross (Navy Cross or Air Force Cross)
Distinguished Service Medal
The President of the United States or any former President of the United States.
Any former member of the Armed Forces who served on active duty (other than for training) and who held any of the following positions:
An elective office of the U.S. Government
Office of the Chief Justice of the United States or of an Associate Justice of the Supreme Court of the United States.
An office listed, at the time the person held the position, in 5 USC 5312 or 5313 (Levels I and II of the Executive Schedule).
The chief of a mission who was at any time during his/her tenure classified in Class I under the provisions of Section 411, Act of 13 August 1946, 60 Stat. 1002, as amended (22 USC 866) or as listed in State Department memorandum dated March 21, 1988.
Any former prisoner of war who, while a prisoner of war, served honorably in the active military, naval, or air service, whose last period of military, naval or air service terminated honorably and who died on or after November 30, 1993.
The spouse, widow or widower, minor child, or permanently dependent child, and certain unmarried adult children of any of the above eligible veterans.
The widow or widower of:
a member of the Armed Forces who was lost or buried at sea or officially determined to be missing in action.
a member of the Armed Forces who is interred in a US military cemetery overseas that is maintained by the American Battle Monuments Commission.
a member of the Armed Forces who is interred in Arlington National Cemetery as part of a group burial.
The surviving spouse, minor child, or permanently dependent child of any person already buried in Arlington National Cemetery.
The parents of a minor child, or permanently dependent child whose remains, based on the eligibility of a parent, are already buried in ANC. A spouse divorced from the primary eligible, or widowed and remarried, is not eligible for interment.
Provided certain conditions are met, a former member of the Armed Forces may be buried in the same grave with a close relative who is already buried and is the primary eligible.
Arlington is reserved for twenty year or combat vets from any war in any service or those approved of after review. All vets get a spot in a military cemetary or a spot in a civilian cemetary that was purchased by the VA for this purpose. They are currently trying to get another plot built in Washington state, since they are ful and all on one side of the state.