entering into safeik sakana to save someone else from vaday sakana

Yaakov was certainly aware of the animosity the brothers had for Yosef, so why did he send Yosef to check on them. throwing him into the lion's den, so to speak?  B'pashtus you could say that Yaakov underestimated the level of animosity and danger.  Sibling rivalry is not uncommon, but it seldom leads to what happened to Yosef.  The Hadar Zekeinim (from the Baalei HaTos') on the parsha quotes another interesting answer from Ibn Ezra:

וא״ת מה ראה יעקב לשלחו לאחיו הלא יודע ששונאים אותו. ואומר אבן עזרא לפי שהלכו במקום סכנה לרעות כי הרגו אנשי שכם. אמר יעקב שמא יענישו לך ספק הוא ושיהרגום אנשי שכם אם ימצאום ודאי הוא ומוטב ליקח הספק מן הודאי לך אמור להם שישובו פן יכום אנשי שכם מכת חרב.

Yaakov perceived the Shechem was a dangerous place for his family to be.  Recall that he did not support the attack on Shechem, fearing that there would be retribution.  When he heard the brothers had taken the sheep to graze near Shechem, he felt that better to send Yosef after them and expose him to some level of risk in order to remove the brothers from certain danger.  

It seems that a person can place himself in safeik sakana to save someone else from a vaday sakana.

This point is debated by others.  The Mishna in Makos (11b) writes that even a great general like Yoav who is needed by the nation is not allowed to leave the ir miklat lest the goal ha'dam attack him  ואפי' ישראל צריכים לו ואפי' שר צבא ישראל כיואב בן צרויה אינו יוצא משם לעולם. The general faces a safeik sakana, but the war is a vaday sakana.  According to the chiddush of Ibn Ezra, why should he not leave the ir miklat?

(Just to add: I don't think the argument advanced by Yehudah in next week's parsha, as explained by Rashi 43:8, to allow Binyanim to travel with the brothers to Egypt is relevant here.    בנימן ספק יתפש ספק לא יתפש, ואנו כולנו מתים ברעב אם לא נלך. מוטב שתניח את הספק ותתפש את הוודאי.  In that case Binyamin was not being put in a safeik sakana to save others, as if he did not go down to Egypt he would be in as much a vaday sakana of dying from hunger as the rest of the family.)