I am an exclusive istockphoto contributor. I know i can upload photos to Alamy as RM . But i wonder can ı upload  the photos those got rejection on Istockphoto to Alamy as RM?

According to iStock's exclusive ASA, you must ask for permission for the rejected image to be released.
Normally, I have got that permission graciously. But it depends which CR person answers your ticket, I've also had, "Yes, you don't need to ask for permission" (once) after asking on a previous occasion if I could just have a blanket permission to save me asking their permission every time (I was told that wasn't possible). Once I was told I'd have to delete any similars from iStock (where does it say that in the ASA?) and once I got a long convoluted story about how I'd have to give up exclusivity and remove any similars.

Alamy sell just fine. Well worth the time. Keywording is crucial though - spamming will bite you in the backside.

Yes, they sell fine! but in very, very few areas and my areas, industry, engineering, technology, certainly isnt one of them. They sell lots of landscapes, travel and scenics. Because Im short of time Im seriously considering stop uploading.