In general it is not a good idea. On top of diseases and parasites that may be transmitted from one species to another (You should also see the following link:
http://www.livingunderworld.org/amphibianArticles/article0007.htmt)
there is also the issue of newt temperament which has to be taken into consideration.
Although Cynops are considered a fairly non-aggressive species, I find that my orientalis can get quite aggressive at feeding time, while the species of Triturus I have are seemingly not as aggressive (I have cristatus). While I am unaware of the temperament of Triturus vulgaris, if they are a calm and easy going newt they may become stressed living with an active and somewhat aggressive newt (at feeding) like Cynops orientalis. There is not much of a size difference between these species so i doubt that one could inflict much damage on the other, but it is still a possibility.
Also it is my understanding that the living requirements of these two species are different -orientalis are more aquatic, needing very little land (perhaps just a floating shelf) while vulgaris are more terrestrial and may require a 50%water:50%land based setup.
tara
I am noticing that the link is not working and that livingunderworld is being updated; just go to
http://www.livingunderworld.org/and click the following links: caudata, amphibian articles, species mixing, new world syndrome.
(Message edited by edwardst on April 26, 2004)