Can workplace IT settings interfere with iCloud bookmark settings?
From this Apple Support document detailing TCP and UDP ports used by Apple software, iCloud uses these ports:

25   - smtp    
80   - http    
443  - SSL (HTTPS)    
587  - Authenticated smtp    
993  - SSL IMAP    
5223 - DAV services


My guess is that it would be port 5223 which being blocked by your company.

As for your company's IT being 'overzealous', they are only doing exemplary due diligence protecting their network and server infrastructure, as well as any user (you) who connects, from nasties out there who would cause harm.