No it is not. Treason is an offense committed on behalf of an enemy during war. Israel is not an enemy and we were not at war at the time.
Russia is now an ally. Would you then believe Robert Hanssen is not guilty of treason and should be given a lighter sentence despite his spying for Russia?
I think that ultimately nobody here knows the whole story, but if the Hersh account is true, than Pollard gave intelligence to the Israelis (about nuclear submarine positioning, communication, etc) that had zero use to Israeli defense and the he must have known was only useful to its ultimate destination, the Soviets.
So, if what the worst said about pollard is true, then the fact that he spied for Israel is irrelevent... he had to know the information was ultimately for the benefit of the USSR.
On another note, is their an offical definition of treason somewhere that backs up what your point?