note that square/circle denote different categories - maybe a better solution would be a revised iconset where icons are less of photo-like images, thus also having more uniform dimensions ?

I think that orange/grey colors of Maintenance/Disabled denote them as well.

Also most of the servers and network devices comes in wide shapes so they are hard to be depicted differently, even if using more symbolic approach.

And the second point is that default zabbix icons are also having the same shape and so the same problem on cramped maps(see next screenshot)

orange already collides with one of the default severity colours, though

as for depicting things in a more uniform dimensions, roberto.moreda once demonstrated some icons to me and i remember liking that a lot - and they had done a great job of "fitting in the box"

I believe that most users just want to create a simple map using default icons with no hassle or little hassle. Anyway, this task is just a suggestion.