I'm not sure how it's setup for the Windows version of ADT, however I'd like to share how to do it for the Mac OS version.
If your only concern is the splash screen and icon, you just have to tweak some files from the bundle.
Note: This is only tested in ADT Version 23 (20140702) downloaded from developer.android.
For the splashscreen
Go to your ADT bundle directory and open the config.ini file located in eclipse/configuration/.
Replace the following:
osgi.splashPath=platform\:/base/plugins/org.eclipse.platform
to this:
osgi.splashPath=platform\:/base/plugins/com.android.ide.eclipse.adt.package
then save the file.
And for the icon
Just edit the info.plist inside eclipse.app/Contents/ and change:
<key>CFBundleIconFile</key>
<string>Eclipse.icns</string>
to:
<key>CFBundleIconFile</key>
<string>adt.icns</string>
lastly, go to eclipse.app/Contents/MacOS and open the file eclipse.ini and modify:
-Xdock:icon=../Resources/Eclipse.icns to -Xdock:icon=../Resources/adt.icns
Hope this helps any Mac OS users of ADT out there.