Actually reading through the previous posts suggests that the question has been answered. As Sister Amy said the ‘all’ is subject to repentance. On the Day of Judgment we believe that faith will ultimately save us by God’s grace, however we may have to be purged of sin first, for those sins we didn’t repent from. Only those who do not have faith will remain in the fire, as the following suggests:
“Whoever says ‘There is no god but Allah’ and has a barley-corn’s weight of good in his heart will come out of the Fire. Whoever says ‘There is no god but Allah’ and has a wheat-grain’s weight of good in his heart will come out of the Fire. Whoever says ‘There is no god but Allah’ and has a atom’s weight of good in his heart will come out of the Fire.” [Bukhari]
Hi Sister Amy
could you please address why Prophet Mohammed would tell his followers to give tidings of hell to Polytheists? Is this still practiced in Islam today to your knowledge? Thank you
Sorry to disappoint you, but I’m not Sister Amy

Though maybe I can help?
The hadith you mention and quoted from the website is as follows:
Salem related that his father said: A Bedouin came to the Prophet and said: O Messenger of Allah my father used to maintain the ties of kinship, and he was so, and he was so. So where is he? He said: In Hell-fire. He said: It was as if that disturbed him, so he said: O Messenger of Allah, where, then, is your father? The Messenger of Allah then said: Wherever you pass by the grave of a polytheist give him tidings of Hell-fire. He said: The Bedouin later accepted Islam and said:The Messenger of Allah has given me an assignment. I would not pass by the grave of a Kãfir except that I would give him tidings of Hell-fire. [Tirmidhi]
Firstly we need to know that the website is a Salafi one and so may have been tampered with. It is unlikely that it is not a hadith, but the translation may be deliberately pointing one in a certain direction, nor does it mention other narrations of the same event (if they were any)
Secondly we need to ask is this a general rule or did it just apply to the Bedouin. If I say to my kids on a rainy day: ‘don’t go outside,’ a few hundred years pass by and then someone tries to ascertain what I meant and decides that I gave an absolute prohibition for all mankind would clearly be wrong. The wording suggest specificity rather than generality. There is extra information about the Bedouin being sad that his father’s good deeds hadn’t saved, that he later converted and then that he had this personal mission. If general, why this extra information? Strange though it may seem, the advice from Muhammad (pbuh) brought the Bedouin to Islam, because he realised that without faith good actions are futile. In terms of legally, no precedent can be taken that Muslims should do this, but it is also clear that it is not impermissible.
Thirdly we need to see are there any other evidences? A general instruction from Muhammad (pbuh) to the whole Muslim community was: "The believer is not one who slanders, curses or uses vulgarity (Tirmidhi). We can see why Sister Amy or most other Muslims wouldn’t have learnt the first hadith since it is a special case and not in keeping with the character of a Muslim.
Lastly we refer the the scholarly tradition and ask what did they say? Well if we refer to the pivotal work on Islamic Jurisprudence Radd al Mukhtar by the eminent ibn A’bideen we see that: it is permitted to curse the unbelievers and sinful in general, though not specifically, except those about whom it is certainly known that they died in a state of disbelief. He further adds that ‘The reality of cursing (la`n) is to distance from Mercy, which cannot be for other than an unbeliever (kafir).’ Which I think sums it up.
On a side point one may say that still seems a little harsh and OK I empathise (NOTE: only permissible not recommended or obligatory!) but then burning eternally is God’s judgment so in some ways it is simply stating the truth, and as the first hadith shows that by cursing the unbelievers it serves as a reminder that unless one change their ways before the grave eternal punishment awaits.
Hope that helps

(still in a rush - sorry)