::::::The report bothers to call them "contracted" fieldworkers, which means their non-member status in AI matters. I understand being "based" in Gaza as residing there, and 99.9% of the population there is Palestinian, but there is no mention of their nationality in the report. Do you see another reasonable interpretation of the word "based" ? We can write "Gaza-based contracted fieldworkers", but I find it more awkard.  
 ::::::NGO Monitor doesn't call itself  "Israeli", nor does WP article about it claim so. Their mailing address is in Jerusalem, but since it's disputed that Jerusalem is in Israel - we might as well call them a Palestinian NGO. I see nothing wrong with "Jerusalem-based NGO Monitor".