The IMA libraries do handle all the companion interactions. If you're using IMA3 as the ad source for an ad-enabled Video Cloud player, the first link you used would be the best resource. I was able to get this working by following that procedure:
https://developers.google.com/interactive-media-ads/docs/companions/companions-gpt
In the Advertising Module of Video Cloud, I set the ad server URL and chose DFP IMA3 as the ad source.
Next, I copied the Javascript publishing code for the player and video from the Media Module's Quick Publish feature.
I then pasted that player code into the of the page code from Example 2, above the for the companions.
To rule out an issue with ad trafficking, I would start out with DFP's Sample ad tag as I did. A sample is available from the DFP VAST inspector:
https://developers.google.com/interactive-media-ads/docs/vastinspector_dual
Currently the sample ad tag provided is below, you can add this as your test player's Ad Server URL in Video Cloud Studio:
http://pubads.g.doubleclick.net/gampad/ads?sz=400x300&iu=%2F6062%2Fiab_vast_samples&ciu_szs=300x250%2C728x90&gdfp_req=1&env=vp&output=xml_vast2&unviewed_position_start=1&url=[referrer_url]&correlator=[timestamp]&cust_params=iab_vast_samples%3Dlinear
If the above test works but your ads aren't, you may need to review what size ad slots you are using and need, and get a bit more into the Google code.
The VAST companions roadblock feature is not active in the case of IMA ad source, so those instructions won't work.
