Saving Yosef by casting him into a pit with scorpions?

Summary: From Chiddushei HaGriz, a solution as to Reuven's intentions and thought-process.

Post: On parashat Vayeshev, R' Yitzchak Zeev HaLevi Soloveitchik cites the pasuk:

24. And they took him and cast him into the pit; now the pit was empty there was no water in it.		כד. וַיִּקָּחֻהוּ וַיַּשְׁלִכוּ אֹתוֹ הַבֹּרָה וְהַבּוֹר רֵק אֵין בּוֹ מָיִם:
now the pit was empty-there was no water in it: Since it says: “now the pit was empty,” do I not know that there was no water in it? For what purpose did the Torah write,“there was no water in it” ? [To inform us that] there was no water in it, but there were snakes and scorpions in it. [From Shab. 22a, Chag. 3a]		והבור רק אין בו מים: ממשמע שנאמר והבור רק, איני יודע שאין בו מים, מה תלמוד לומר אין בו מים, מים אין בו אבל נחשים ועקרבים יש בו:

and then writes:

"But what was the benefit of this? Was not the pit empty with no water in it, but with snakes and scorpions it it, as Rashi brings down upon pasuk 24? And it is explained in the Rambam, perek 9 from Hilchot Melachim that a Ben Noach who kills, etc., or who compels him before a lion, or leaves him in starvation until he dies, since he caused his death, he [the Ben Noach who did this] is killed. End quote. And what is apparent is that, behold, it is stated in Berachot 33a that:

In a certain place there was once a lizard⁷  which used to injure people. They came and told R. Hanina b. Dosa. He said to them: Show me its hole. They showed him its hole, and he put his heel over the hole, and the lizard came out and bit him, and it died. He put it on his shoulder and brought it to the Beth ha-Midrash and said to them: See, my sons, it is not the lizard that kills, it is sin that kills!

And because of this, Reuven felt certain that the snakes and scorpions would not kill Yosef, and as was indeed so afterwards, that they did not cause him harm."

This is a neat resolution of this difficulty. See other approaches to solving it in this parshablog post. For example, they were unaware of the presence of snakes and scorpions.

I wonder, for Rabbi Chanina ben Dosa was without sin. Was Yosef also so, and did Reuven believe it to be so? I'm not asking whether he deserved death, but whether he was sufficiently righteous that his safety before snakes and scorpions was so assured. Consider these Rashis, at the start of the parasha:

and he was a lad: He behaved childishly, fixing his hair and touching up his eyes so that he would appear handsome. [From Gen. Rabbah 84:7]

והוא נער: שהיה עושה מעשה נערות, מתקן בשערו ממשמש בעיניו, כדי שיהיה נראה יפה:

tales about them: Heb. דִּבָּתָם Every expression of דִּבָּה denotes parlediz in Old French, gossip, slander. Whatever evil he could tell about them he told. דִּבָּה is an expression of making the lips of the sleeping speak (דוֹבֵב).

דבתם: כל לשון דבה פרלידי"ץ בלע"ז [רכילות] כל מה שהיה יכול לדבר בהם רעה היה מספר:

That is, was the being spared from the snakes and scorpions due to personal righteousness, or due to fullfillment of the Divine plan, declared at the bris bein habetarim?