"So, is there a statute of limitations for UCMJ prosecution?"
I'm not a legal expert.
Maybe this is why he has a trial lawyer as a VP candidate. LOL
http://www.constitution.org/mil/ucmj19970615.htm
* 843. ART. 43. STATUTE OF LIMITATIONS
(a) A person charged with absence without leave or missing movement in time of war, or with any offense punishable by death, may be tried at any time without limitation.
(b)
(1) Except as otherwise provided in this section (article), a person charged with an offense is not liable to be tried by court-martial if the offense was committed more than five years before the receipt of sworn charges and specifications by an officer exercising summary court- martial jurisdiction over the command.
(2) A person charged with an offense is not liable to be punished under section 815 of this title (article 15) if the offense was committed more than two years before the imposition of punishment.
(c) Periods in which the accused is absent without authority or fleeing from justice shall be excluded in computing the period of limitation prescribed in this section (article).
(d) Periods in which the accused was absent from territory in which the United States has the authority to apprehend him, or in the custody of civil authorities, or in the hands of the enemy, shall be excluded in computing the period of limitation prescribed in this article.
(e) For an offense the trial of which in time of war is certified to the President by the Secretary concerned to be detrimental to the prosecution of the war or inimical to the national security, the period of limitation prescribed in this article is extended to six months after the termination of hostilities as proclaimed by the President or by a joint resolution of Congress.
(f) When the United States is at war, the running of any statute of limitations applicable to any offense under this chapter--
(1) involving fraud or attempted fraud against the United States or any agency thereof in any manner, whether by conspiracy or not;
(2) committed in connection with the acquisition, care, handling, custody, control, or disposition of any real or personal property of the United States; or
(3) committed in connection with the negotiation, procurement, award, performance, payment, interim financing, cancellation, or other termination or settlement, of any contract, subcontract, or purchase order which is connected with or related to the prosecution of the war, or with any disposition of termination inventory by any war contractor or Government agency;
is suspended until three years after the termination of hostilities as proclaimed by the President or by a joint resolution of Congress.
*(g)
(1) If charges or specifications are dismissed or insufficient for any cause and the period prescribed by the applicable statute of limitations--
(A) has expired; or
(B) will expire within 180 days after the date of dismissal of the charges and specifications, trial and punishment under new charges and specifications are not bared by the statute of limitations if the conditions specified in paragraph (2) are met.
(2) The conditions referred to in paragraph (1) are that the new charges and specifications must--
(A) be received by an officer exercising summary court-martial jurisdiction over the command within 180 days after dismissal of the charges or specifications; and
(B) allege the same acts or omissions that were alleged in the dismissed charges or specifications (or allege acts or omissions that were included in the dismissed charges or specifications).
Failure to be charged with a crime is not proof of innocence. While I can not in reality expect Hanoi John to be charged now, that does not negate the fact that - by his own admission - he did commit the crimes.