They can testify.
There may be issues about credibility, especially if there is evidence of "planting drugs."
Get a good criminal defense lawyer from that area. It's quite possible H/she knows the officer and his history if they do a lot of drug cases in town.
This is not the place to analyze complex issues like this. You need a Defense Attorney to look at your case, do a proper intake, and explain to you what your options are. Spend you energy looking or an attorney you trust. You should also stop posting facts about your case online.
Absolutely they can. Of course ther could be some credibility probllems. But you need to hire an attorney.
The above is not intended as legal advice. The response does not constitute the creation of an attorney client relationship as this forum does not provide for a confidential communication.