Firstly one has to understand that the institution of this heavenly graveyard was a prophecy of the Holy Prophet Muhammad(saw).
There is a Prophecy in regards to the latter day Messiah recorded in Sahih Muslim which states:
يُحَدِّثُهُمْ بِدَرَجَاتِهِمْ فِي الْجَنَّةِ
“would inform them of their ranks in Paradise” (Sahih Muslim, Book 54, Hadith #136)
The way this beautiful prophecy was fulfilled, was with the Heavenly Graveyard. Hazrat Mirza Ghulam Ahmad(as) said:
Some twenty to twenty-five minutes before the time of the (Fajr) Prayer, I saw in a dream as if I had purchased a piece of land for the purpose of converting it into a graveyard for our Jama‘at. I was told that its name would be Maqbarah Bahishti, meaning that whoever is buried there would be admitted to Paradise. Then I saw that some old gospels had been discovered in Kashmir which would break the cross. I proposed that some persons should go there and bring those gospels so that a book could be written about them. Hearing this Maulavi Mubarak ‘Ali declared his readiness to go but requested that a place should be kept for him in the Maqbarah Bahishti. I said: Khalifah Nur-ud-Din should also be sent with him….
The Promised Messiah(as) continued: Sometime back I had planned that there should be a separate graveyard for our Jama‘at. God has now approved of my plan. Injil [Gospel] means good news. It would seem that God intends to manifest some great news from Kashmir and that the person who would carry through this task would certainly enter Paradise. (Tadhkirah Page 566, [al-Badr, vol. 1, no. 5 and 6, November28 and December 5, 1902, p. 35 and al-Hakam, vol. 6, no. 42, November 24, 1902, p. 4] )
This graveyard itself was the fulfillment of the Prophecy. Ahmad(as) states:
The third condition is that a person who seeks burial in this graveyard should be righteous and should refrain from all that is forbidden and should not indulge in anything which has a smattering of associating others with God or of an innovation. He should be a true and plain Muslim. Every righteous person who possesses no property and can render no financial assistance can be given burial in this graveyard if it is proved that he had devoted his life to the faith and was in every way a righteous …….
It would not he enough to contribute one tenth of moveable and immovable property but it would be necessary that the testator should, as far as is possible for him, act upon Islamic commandments and should strive after righteousness and purity and should have sincere faith in the Holy Prophet and should not contravene the rights of his fellow creatures. (Al-Wassiyyat, p.24)
The means of this was not only in regards to financial matters, rather of living a life full of purity and righteousness.
There is no allegation against this which can possibly exist. There is nothing wrong with a prophet conveying good news of paradise to their followers. It is narrated in Bukhari:
Narrated Abu Huraira:That heard Allah’s Messenger (ﷺ) saying, “We are the last but will be the foremost to enter Paradise).” The Prophet added, “He who obeys me, obeys Allah, and he who disobeys me, disobeys Allah. He who obeys the chief, obeys me, and he who disobeys the chief, disobeys me. The Imam is like a shelter for whose safety the Muslims should fight and where they should seek protection. If the Imam orders people with righteousness and rules justly, then he will be rewarded for that, and if he does the opposite, he will be responsible for that.”(Sahih Bukhari, Volume 4, Book 52, Hadith #204)
He(saw) also conveyed the news of Paradise to ten of his companions which is clearly known to many Muslims as the Ashra Mubasharah. The Holy Prophet Muhammad(saw) also initiated a graveyard called Jannatul Baquee which means the heavenly graveyard as well. The graveyard initiated by the Promised Messiah(as) was the outcome of divine revelation by Allah and a fulfillment of the hadith of Sahih Muslim. There is no possible objection against this.