Hoshea refers three times to J, in 9:10, in 12:13, and in 2:20. He refers three times to E and J together, in 12:4, in 12:5, and in 4:3.
The verse 12:7 contains a hint to E (
בֵּאלֹהֶיךָ תָשׁוּב) including the name Elohim, but this is in the context of 12:6, which clearly proclaims the name Hashem,
וַיהוָה, אֱלֹהֵי הַצְּבָאוֹת--יְהוָה, זִכְרוֹ
It seems to be on purpose, 12:6-7 is a hint to
וְהָיָה יְהוָה לִי, לֵאלֹהִים, which is from E, but an explicit separate reference to E, and to E alone, does not seem to exist in Hoshea. Especially, what follows in E,
וְהָאֶבֶן הַזֹּאת, אֲשֶׁר-שַׂמְתִּי מַצֵּבָה--יִהְיֶה, בֵּית אֱלֹהִים, is only hinted at (perhaps) by Beth-El. An explicit reference to what existed in Beth-El, the Matzevah, is off limits to Hoshea. It can be seen as a sign of Hoshea's awareness, that the time of E, and its Matzevot, which had made the people of Israel misunderstand (11:7), is over (10:1,2 and 3:4), and that E and J must go together.