About this issue I agree with those who say 'call SAFE and - if requested - go for help to your partner'.
BTW in a game I saw 1 month ago a very difficult situation occurred:
Bottom of VII
Home team down by only a run (can't remember... something like 2-3 or so)
Runner on 3rd
Two outs
BU is of course positioned behind 2-3
line
Batter hits a gounder to SS and the subsequent throw was not perfect
1st baseman had to move a little in the direction of home
There was a swipe tag (very very fast and with BR very close to 1st base)
BU called SAFE (because NOT sure about the tag and used also the pointing to say BR was safe because of
pulled foot)
Now defensive coach asked TIME and go to BU, saying BR was out because of the tag and asking him to go for help to his partner
Two umpires had a little talk and PU convinced BU the tag was real and effectively BR was out...
'Have the right call' was the filosophy of BU... game end.
They needed an escort to reach dressing rooms...
Ciao
P.S. Sometimes I hate two-umpire-system... because of this kind of problems!!!