Our Made for TV platform supports DFP video pre-roll via the VAST tag you put into the "Advertising & Analytics" section of the labs page:

Currently only Roku supports DFP. We do not leverage the Roku Audience network. Make sure your ad response is VAST 2.0 or 3.0 and NOT VMAP.
Testing your ad tag
Before putting your VAST URL into our back end please test it using the Google VAST ad tag tester tool. The tool can be found here.
Once you click on the "TEST AD" button, scroll down to the "Events" section. Make sure the output of the events includes a sentence stating that the ad server returned a valid ad.
Ad Cadence
There is no restriction on ad length, but we recommend short as possible since most VOD clips are short.
Our pre-roll DFP request cadence is as follows:
- First video play free (no ad)
- pre-roll ad request before 2nd video
- pre-roll ad request before every 3rd video
It is up to your DFP configuration on if/when the ad is filled. The cadence above is just when we request a DFP ad - it is up to your DFP configuration to fill the add (if at all).