There's a free jobs submission form but no contact details that I could find for the jobs123 network. All the linked sites look like they've been set up with blogging software, nothing wrong with that per se, but it does look a bit amateurish. Since it doesn't look like jobs123 themselves are a recruitment agency - they just provide a facility for employers to post jobs - there's not really a questionmark whether they're any good or not as a recruitment agency. Presumably, when jobs123.com gets a job submission, they just post it on one of their many job websites.
Think of jobs123.com as more like a classified ads network rather than an online recruitment agency. Their apparent claim of collecting all job websites is a bit hollow considering they don't list any of the more well known Dubai job websites. For example this is what someone from jobs123.com requested in another forum (and then proceeded to list only jobs123.com sites, but none of the others that were suggested).
I'm building a list of jobsites in Dubai. If you recommend a site please let me know by responding to this and I'll add it to the list.
As far as I can tell, all these websites are jobs123.com offshoots.