Ahh!! Finally!! i was trying stuff like .separator and .ux-menu-link-level-0 separator... and was trying on the menu.php instead of the template css, was so confused...
Unfortunatly it changes only the color of the item letter and it's keeping the other menu itens css. The background is orange and when you hover it's white, that needs to be changed to always grey, but i think i'll figure it out from here anyway. DOn't have much time to be trying now, but i'll try so later.
Thank you for the awesome support and sorry if i was a big bother!! And the suggestion stays, i guess, for the future to have support for this separator feature on ARI Ext Menu extension.
Best of luck, thanks again!