Firstly this is a great thread. I have often wondered who the big influencers were in the zoo world. Maybe we need to look at different categories of influence. The pioneers of modern zoo (which include many of the names on your original list) and possibly another list of major (secondary?) influence (Fleay and Wayre would probably fall into this).
Also what about people outside the West? Bernard Harrison for Singapore (first Night Safari)? What about Africa or South America? And any women who made a lasting mark?
I'd say with some regret that South America / Latin America hasn't yet produced anything uniquely its own in terms of zoos as it has mainly looked to the United States and Europe for models on which to base its institutions (and at least one of the directors of one of the more famous zoos of the region , Chapultepec zoo, was also a European). In my opinion , some of these zoos actually succeed in doing a better job in conservation and education , despite a chronic shortage of resources and funding , have more "heart" than your average European or American zoo (and also noticeably lack the institutional arrogance present in some of the former institutions).
From what I've seen IMO the closest thing to a uniquely regional vision of a zoo would have to be two zoos that I've seen and know of : Zoológico Miguél Álvarez del Toro / ZOOMAT (Mexico) and Zoo Gramado (Brazil). I suppose I would consider them to be unique because they both depart from the practice of keeping exotic species and instead have a vision and ethos that centres on the conservation of native Mexican and Brazilian species and educating visitors about the importance of conservating natural habitat.
In the case of ZOOMAT it was founded by a famous and charismatic Mexican biologist / conservationist Miguél Álvarez del Toro. Although I wouldn't put him in the same category as a Gerald Durrell or Peter Scott, at least in terms of impact, I do think that Del Toro certainly had a strong and individual vision of what he felt a zoo should be and do and so was a fellow traveller of sorts (albeit his legacy in conservation was local / regional rather than global). Gramado zoo on the other hand is a much younger institution (founded 2008) and is still "up and coming". However, purely in terms of its mission and ethos in terms of conservation and education and overall impact it is definitely IMO among the best zoos in Latin America.
There have been some and there are some incredible women in positions of power at zoos who have made a lasting mark on the development of these institutions in regards to a stronger and greater conservation ethos within the organizational culture. I can give two examples of this at two of the best zoos of Latin America that I have personally seen ,I know them personally, and they have in one capacity or another been my coordinators and mentors:
Erika Servin Zamora (Chapultepec zoo , Mexico city , Mexico) - Has helped radically overhaul the zoo and direct it from being a more old fashioned institution focused on exhibiting "ABC" species and being a recreational attraction towards being at the cutting edge and contributing greatly to ex-situ and in-situ conservation. This particularly with regards to that of native species such as the Axolotl, the Californian condor , the Mexican wolf and several other species. Erika studied at the DESMAN (not sure if thats the right spelling ? ) programe at Jersey zoo in the UK and has done some truly amazing things in terms of conservation.
Cecilia Lembra (Sorocaba zoo , Sao Paulo state, Brazil) - Has been the driving force of the development of conservation programes at the zoo for over three decades now and has helped develop ex-situ conservation programes for endangered and endemic Brazilian species like the Southern Muriqui , Golden lion tamarin , maned wolf and several others. Also encouraged research programes for students, sustainable culture and environmental education programes with the visitors that have been highly successful. Cecilia also studied at the conservation course of Jersey zoo back in the UK back in the early 1990's (I think it had a different name from DESMAN back then but I'm not sure). Once again she has done some incredible and wonderful things in terms of implementing conservation in Brazil and she will continue doing them.