Scio tibi eum non esse odio

I’ve been reading some of Caelius’ and Cicero’s correspondence (to mixed success) and am unsure about a sentence in letter 88 (in the Loeb numbering)/VIII.6 (in the traditional).

Scio tibi eum non esse odio.

Is the “odio” a dative of purpose? “I know that he is not as hatred/a hated man? to you”. Or I guess as a double-dative? The meaning is obvious but I can’t quite parse it.

Yes, this is the so-called double dative construction: a dative of “purpose” and a dative of reference. It shouldn’t be hard to parse, but translating is somewhat tricky.

“I know that he is not [as] [a source/object of] hatred to/for you.”

See Allen & Greenough sec. 382.1 and Note 1:

http://www.perseus.tufts.edu/hopper/text?doc=AG+382&fromdoc=Perseus%3Atext%3A1999.04.0001

  1. The Dative is used to denote the Purpose or End, often with another Dative of the person or thing affected.

This use of the dative, once apparently general, remains in only a few constructions, as follows:—

The dative of an abstract noun is used to show that for which a thing serves or which it accomplishes, often with another dative of the person or thing affected:—

“reī pūblicae clādī sunt ” (Iug. 85.43) , they are ruin to the state (they are for a disaster to the state).
“māgnō ūsuī nostrīs fuit ” (B. G. 4.25) , it was of great service to our men (to our men for great use).
tertiam aciem nostrīs subsidiō mīsit (id. 1.52), he sent the third line as a relief to our men.
suīs salūtī fuit (id. 7.50), he was the salvation of his men.
“ēvēnit facile quod dīs cordī esset ” (Liv. 1.39) , that came to pass easily which was desired by the gods (was for a pleasure [lit. heart] to the gods).

[*] Note 1.–This construction is often called the Dative of Service, or the Double Dative construction. The verb is usually sum . The noun expressing the end for which is regularly abstract and singular in number and is never modified by an adjective, except one of degree ( māgnus , minor, etc.), or by a genitive.

Odiō is datiuus finalis. Often datiuus finalis goes together with datiuus (in)commodi or an indirect object. Here are some examples from a grammar (Sjöstrand), with exactly corresponding phrase at the end:

alicui auxilio esse ‘be of help to someone’
esse alicui impedimento ‘be (of) obstacle to someone’
Haec res omnibus saluti fuit ‘This is of salvation to everyone’
Cui id bono est? ‘Who benefits from it?’
Omnes, qui mihi cordi sunt ‘All who are dear to me’
Odio sum Romanis. ‘I am hated by the Romans’

Thanks very much to the two of you.

Is this an example of double dative as well? Tibi auxiliō esse possum. I saw it in the Latin Assimil sans Peine. I understand the meaning, but am confused why it is in the dative. What’s the literal translation behind it?

Yes, it is. Another famous example: cui bono? A possible literal translation of your example:

I can be for aid to thee.

Gratias maximas tibi ago, mi Beduere!