As long as they haven't represented another country in Davis Cup, then the 3yr rule is exempted.
34. ELIGIBILITY OF PLAYERS
Any tennis player who is in good standing with his National Association in accordance with Appendix D shall be qualified to represent that country if he:
(a) Is a national of that country, has a current valid passport of that country, has lived in that country for 24 consecutive months at some time and has not represented any other country during the period of 36 months immediately preceding the event.
If a player is qualified under this sub section to represent more than one country and the National Association of one of those countries wishes to nominate him to represent it, that Association shall submit an application to the ITF, with a copy to any other National Association concerned. Such application must be received by the ITF at least six months prior to the event for which the player wishes to be nominated.
The Davis Cup Committee will give a ruling having taken into account all relevant matters.
(b) (i) A player who has represented, or has been eligible to represent a country and such a country is divided into two or more countries, shall immediately be eligible to represent any one of those countries.
(ii) A player who has represented, or has been eligible to represent a country and such country is absorbed in whole or in part by another country, shall immediately be eligible to represent such other country.
(c) A player shall be deemed to have represented a country if he shall have been nominated, and shall have accepted, the nomination to play in the Olympic Games Tennis Event or in any International Team Competition recognised by the ITF and listed in Bye-Law 2.1(a).
(d) A National Association may appeal to the Board of Directors to nominate a player who is not eligible under the above Rules and the Board of Directors may agree the application if the full circumstances warrant an exception being made. Such application must be received by the ITF at least six months
prior to the event for which the player wishes to be nominated.
(e) The Davis Cup Committee has the right to ask a National Association to produce evidence to show how a player is qualified to represent that country.
Note: A player who represented a country under the Rules in force in 1994 or prior thereto, shall continue to be eligible to represent that country even if he is no longer qualified to do so under the amended terms of this Regulation.