Ulwarth's name seems to come from an Easterling dialect, and is not therefore directly translatable. However, his father Ulfang's name can be interpreted ulf fang, 'wolf fang', and so following that scheme Ulwarth's initial ul- may derive from the 'wolf' of his father's name. Assuming that is correct (which is far from certain), warth is still difficult to interpret; it possibily comes from a word like weorÞ, which could broadly be understood as 'lord' or 'leader' in this context.
The Etymologies (in volume 5 of The History of Middle-earth suggest an alternative interpretation, whereby Ulwarth is an Elvish name translatable as 'hideous betrayer' (and must therefore have been given to him by the Elves after the Nirnaeth). However in The Lhammas (in the same volume) the name is explicitly said to come from a lost language. Clearly one of these conceptions must have superseded the other, but it's uncertain which was intended as the final version.