Sentiment Analysis: Train Separate Models or Use One for All
I would suggest that you train a single model. The features correlated with positive or negative sentiment in a review are likely the same as those in a survey response. That is, “good” means good in both, “bad” means bad in both. 

In general you should combine models and datasets when you think that the features in the different situations have the same meanings/interpretations. If they have contradictory or different meanings/interpretations, then you should consider training separate models.