Tentativeness vs Hedging

On the one hand, hedging is taking a restrained position on the possibility that something else might be true - leaving the door open for other possibile conclusions your research might support in the alternative; but on the other hand, tentative is taking a more restrained position than the evidence might support to avoid being seen as sticking one's neck out - hesitant to take a strong opinion, for fear of looking bad or through risk avoidance.

But I might be wrong.

Although I'm pretty sure I disagree with your characterization of hedging as necessarily polite - sometimes it can be weasly.

Hedging limits risk. You might understand "hedging" better in the context of betting, where the word is often used. For example, if I bet a lot of money on a team to win a baseball game, and later I decide I shouldn't have bet so much, I might bet on the other team to win. That's called "hedging" a bet.

Insurance is also sometimes referred to as "hedging" - your are limiting your risk.

When you make a statement in such a way as to protect yourself from the risk of being wrong, that's hedging. For example, adding "I think that..." to the beginning of a sentence or "... but I could be wrong" at the end of it. A common way that professional advisors hedge is by saying "that should work" instead of "that will work."

As stated above, speaking tentatively might involve hedging, but it could also describe other forms of speaking without confidence, like speaking softly.

Tentative expresses uncertainty, the idea that the results of research are provisional, or that researchers are not confident a conclusion or forecast is correct.

A research conclusion may be expressed with considerable certainty, but readers may be cautioned that there are conditions under which the results may not hold or that the results are valid only for the groups or areas studied. “However” is a word that may introduce such hedging.. A researcher may have confidence in a forecast or prediction provided that (for example) vaccines are indeed successful in controlling Covid-19.

One might argue that a great deal of the difference is in the writing.

Tentativeness is a more abstract and general quality:

Done without confidence; hesitant. Lexico

Whereas hedging is a technique that might be used by someone who is tentative:

Limit or qualify (something) by conditions or exceptions. Lexico

Although the two tend to go together, one might, for example, be tentative simply by making common or easily-proven claims, without hedging them. And one might make some claims that are so bold as to seem that they couldn't be called "tentative", but nevertheless still "hedge" those claims by making them conditional or otherwise non-universal.