In a recent paper which will be published in Romania, it is said that these names are in fact corrupted latin.
Arcaragantes, likely corrupted form from "arcera gentis" (people with carriages, "arcera", that is what these nomads used to travel)
Limigantes, likely from "limitis gentis", "people of the border", if considering the fact that the place in which these "limigantis" are mentioned (and archeologically identified as a mixed local dacian/sedentarized iazigii) are exactly on some great earth walls which cover much of eastern Hungary and Western Romania...
About iranian elements, if one reads carefully Ammianus Marcellinus, there is one place it is mentioned a shouting "arha! Marha!", that likely means "Death! Death!" in the language of the iazigii. Also, iranian toponymes
survived to the present day in western Romania : Zarand, Tamand, Zerind, Carand, Bihor, possibly even the name Arad...
There is much more to say upon this subject,
Alexandru B