Are we talking important in the sense they were not all powerful late war models, or that they have no important place in this game? 
They didn't make many, their tanks never really had an impact on the outcome.
If you model a decent early war light tank or Italian tank you'd have a good proxy for Japanese armor. Unless the modeling could be done quickly and cheaply, I'd not waste any resources on armor for the Itais or the Japanese. I think the Chi-Ha type 97 was their best tank that they made in any quantity and they made how many of those? 1,000? 2k, 3k? Their later tank designs never made it since they had no steel to make them. You could model either the Chi-Ha or one of the Fiat tanks and basically have a good enough proxy for all Japanese and Italian armor. I don't know if they built 10,000 tanks that were used in warfare between them both. As with aircraft, both nations did not have the resources to field the very finest designs quickly enough or in enough numbers to make a difference (that and a critical shortage of properly trained pilots on Japan's part).
