Is it permissible for a non-Muslim or an infidel from other faiths to attend and stand during the funeral prayer with the Imam?

Yes, Muslims are to prevent a Dhimmi from accompanying a Muslim's funeral procession because he is ritually impure, and the angels of mercy flee from him. Also, the purpose of accompanying a funeral procession is to intercede for the deceased, and a disbeliever is not worthy of that or of forgiveness. Furthermore, accompanying funeral processions is a communal obligation (fard kifaya) and one of the rituals of Islam, and a disbeliever is not among those obligated by it. Moreover, a disbeliever accompanying a Muslim's funeral procession would be a favor from the disbeliever to the Muslim, and that is an act of alliance with the disbeliever. Allah Almighty says: "And never will Allah grant to the disbelievers a way (to triumph) over the believers" and "O you who have believed, do not take the Jews and the Christians as allies." This would please the disbeliever and cause him to gloat over the Muslim, and it involves glorifying the disbeliever, whereas what is obligatory is to humiliate and demean him. If a disbeliever is prevented from walking with those accompanying the funeral, then preventing him from standing for the prayer is even more appropriate.