As per the information on, Travelling to Latin America to take hallucinogenic drugs: how does one do it safely?
Peru and Brazil allow such usage, but it's not clear on their Import & Export laws. US courts have allowed limited religious usage to certain followers of such faiths, but entry & exits have examples of people being arrested by BCP (as was in the case of a Colombian Shamanic healer).
I have friends in the Mexico City area who also follow similar rituals.
This was the first source of information on legalities across places which have not explicitly allow or legalized it for general or specific purposes.
Internationally, DMT is a Schedule I drug under the Convention on Psychotropic Substances. The Commentary on the Convention on Psychotropic Substances notes, however, that the plants containing it are not subject to international control:
The cultivation of plants from which psychotropic substances are obtained is not controlled by the Vienna Convention. . . . Neither the crown (fruit, mescal button) of the Peyote cactus nor the roots of the plant Mimosa hostilis nor Psilocybe mushrooms themselves are included in Schedule 1, but only their respective principals, mescaline, DMT, and psilocin.
A fax from the Secretary of the International Narcotics Control Board (INCB) to the Netherlands Ministry of Public Health sent in 2001 goes on to state that "Consequently, preparations (e.g. decoctions) made of these plants, including ayahuasca, are not under international control and, therefore, not subject to any of the articles of the 1971 Convention."
Despite the INCB's 2001 affirmation that ayahuasca is not subject to drug control by international convention, in its 2010 Annual Report the Board recommended that governments consider controlling (i.e. criminalizing) ayahuasca at the national level. This recommendation by the INCB has been criticized as an attempt by the Board to overstep its legitimate mandate and as establishing a reason for governments to violate the human rights (i.e., religious freedom) of ceremonial ayahuasca drinkers.
It would be interesting and key to research the specifics of Nations and their viewpoints / approaches to such.