Could this concern about getting tainted by Trump keep anyone considering a run in 2020 away from Trump (including not wanting to even be vetted as his VP). Would even perfunctory 'I support the nominee of the party' type of endorsements be problematic?
Probably not on that last part. The people who are really wishy-washy, and just offer a perfunctory "I support the nominee" will probably be in the least trouble, because they won't offend most people on either side of the Trump schism.
However, people who spend too much time talking up Trump and defending him will be putting themselves at political risk, which goes quadruple for whoever agrees to be his running mate. That's why many potential veep candidates will not agree to be vetted, and it's why you've already seen several people try to preemptively take themselves out of consideration. Many GOP politicians will endorse Trump, yet still not want to be his running mate, or even appear on the same stage as him.