¶ Vine Helper's stance
In all honesty, Vine Helper does its best to abide by Amazon's Conditions of Use, Amazon's Community Guidelines, and the specific Terms and Conditions set out for the Amazon Vine program. Many of the ideas and features are not implemented and/or developed for Vine Helper because they would go against some rules, announcements and warnings made by Amazon Vine in the past, and we hope to stay well within the boundaries set by Amazon.
Vine Helper, as a devlopement team, also firmly believes in fairness among Vine members, and as a result, do not develop Vine Helper in a way that is seen as gaining an advantage over other users.
¶ Amazon's stance
Our attempts to obtain clarifications on the Conditions of Use as well as the Terms and Conditions have not been successful. The interpretation of such stipulations is strictly up to Amazon (in any way they see fit), so it is possible that they are purposefully staying ambiguous to avoid creating any precedent.
It is also not expected that Amazon or the Amazon Vine Team will officially take a stance in supporting Vine Helper (or any other extension for that matter), just like how they don't take a stance in supporting your favourite translation extension.
With cases of customer support, it is very likely that they aren't aware of what Vine Helper is or does, and as a result, just take the easy way out by saying they don't support it. People have attempted asking the Amazon Vine Team to mixed results, so it's possible there is no unified answer even among agents when it comes to whether extensions are allowed.
The screenshot below was obtained by an individual asking specifically about Vine Helper and Vine Discord, which seems to suggest that despite there being no official support from them, they are not seen as an issue:
Note that the validity of this screenshot has not been officially confirmed, but is not believed to have been forged or altered aside from censoring of the individual's name and the red square highlighting the language and the source of the email response.