Actually yes it is (details here http://msdn.microsoft.com/en-us/library/microsoft.sharepoint.spsecurableobject.hasuniqueroleassignments(v=office.14).aspx). One important note though - simple Load statement with a ListItemCollection parameter (i.e. ctx.Load(lic)) does not load 4 properties of ListItem by default when you return list items: DisplayName, EffectiveBasePermissions, HasUniqueRoleAssignments, and RoleAssignments. If you tried to reference them in your code, you will get a Property not initialized error.
To get beyond that you need to specifically ask to have them included when you define your query using, by example the IncludeWithDefaultProperties
function retrieveProperties () {
var clientContext = new SP.ClientContext('/sites/TestWebs/TestWeb1');
this.oWebsite = clientContext.get_web();
clientContext.load(oWebsite, 'Title', 'HasUniqueRoleAssignments');
clientContext.executeQueryAsync(Function.createDelegate(this, this.onQuerySucceeded), Function.createDelegate(this, this.onQueryFailed));
}
function onQuerySucceeded() {
alert('Title: ' + oWebsite.get_title() +
'\nUnique role assignments: ' + oWebsite.get_hasUniqueRoleAssignments());
}
function onQueryFailed(sender, args) {
alert('Request failed. ' + args.get_message() + '\n' + args.get_stackTrace());
}