EnterWorks does support validation assigning validation rules to repeatable attributes.
To assign or unassign an existing validation rule to an attribute:
In the Feature bar, under the Content tab, select a repository based on the desired profile, click the arrow to the right of Manage Model and select Profile.
The Profile editor will open. Click Next at the bottom of the page to move to the Define Attributes page.
Find the attribute you wish to assign to a validation rule and double-click to open it in edit mode.
The top of the editor lists configuration options. Near the bottom of the editor is the Define Attribute Rules section. From the Action dropdown, choose Assign.
A list of rules will appear. Select one or more rules you wish to assign to the attribute. Note that if the attribute is multi-language, the rule may only apply to certain language versions of an attribute. When you are finished selecting the rules, click OK at the bottom of the page.
You are taken back to the attribute editor window where you will see the newly assigned validation rule.
To detach a validation rule, in the Define Attribute Rules section, select the rule, open the Action dropdown menu and select Detach.
Click OK to return to the Profile editor.
To save your changes, make sure to click Save in the Profile Editor.
Clear the data cache.