This seems to be OK to me, as Dia is Suggested by the Inkscape package, because it adds additional exporting functionality to inkscape, thus is an Add-On to Inkscape. The Software Center explicitly states that a package suggested by another one should be treated as an add-on package of the package suggesting it. See https://wiki.ubuntu.com/SoftwareCenter#Add-on%20packages.
This seems to be OK to me, as Dia is Suggested by the Inkscape package, because it adds additional exporting functionality to inkscape, thus is an Add-On to Inkscape. The Software Center explicitly states that a package suggested by another one should be treated as an add-on package of the package suggesting it. See https:/ /wiki.ubuntu. com/SoftwareCen ter#Add- on%20packages.