An earlier version of this article recommended that the calling
application should dispose of the SPWeb.ParentWeb. This is no longer
the official guidance. The dispose cleanup is handled automatically by
the SharePoint framework.
Also you can find this note:
This best practice addresses the issue identified by the SharePoint
Dispose Checker Tool as SPDisposeCheckID_170.
and this example:
using (SPSite site = new SPSite(http://localhost))
using (SPWeb web = site.OpenWeb())
SPList list = web.Lists["Announcements"];
SPWeb parentWeb = list.ParentWeb; //No explicit dispose required.
As you can see some times dispose checker works incorrect.
In your example you cannot do any harm in disposing of the web. The golden rule is "Did you create the web", i.e. you have based everything off a brand new site/web created on the URL of the feature parent which is a safe way of doing things. Any further webs can be safely disposed of because they only exist due to your code.