I heard that the Prophet, sallallaahu ‘alayhi wa sallam, said that the adulterer is deprived of marrying the Hoor in Paradise. Is this true even if he repents?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu 'alyhi wa sallam, is His slave and Messenger.

There is no doubt that adultery is one of the grave major sins and a most dangerous act of disobedience, and therefore, Allaah The Almighty warned against it in particular verses in the Quran. Likewise, the Prophet, sallallaahu ‘alayhi wa sallam, warned against it in his Sunnah. In this regard, Allaah The Almighty Says (what means): {And do not approach adultery. Indeed, it is ever an immorality and is evil as a way.} [Quran 17: 32]

At the same time, Allaah The Exalted, out of His favor and mercy,

opened the door of repentance to His servants. He The Almighty Says (what means): {Say, "O My servants who have transgressed against themselves [by sinning], do not despair of the mercy of Allaah. Indeed, Allaah forgives all sins. Indeed, it is He who is the Forgiving, the Merciful."} [Quran 39: 53]

Furthermore, Allaah The Almighty describes the characteristics of His true servants in the verse (what means): {And those who do not invoke with Allaah another deity or kill the soul which Allaah has forbidden [to be killed], except by right, and do not commit adultery. And whoever should do that will meet a penalty. Multiplied for him is the punishment on the Day of Resurrection, and he will abide therein humiliated - Except for those who repent, believe and do righteous work. For them Allaah will replace their evil deeds with good. And ever is Allaah Forgiving and Merciful.} [Quran 25: 68-70]

According to these verses, those who commit grave major sins, even those who associate others with Allaah The Almighty in worship, if they sincerely repent to Him and thereafter do righteous deeds, Allaah The Almighty will replace their evil deeds with good ones.

Consequently, any person who sincerely repents from adultery, Allaah The Almighty will accept his repentance and admit him into Paradise wherein there is all that the souls of man desire and that delights the eyes - and this includes the Hoors. 

In brief, whoever sincerely repents to Allaah The Almighty from adultery and does righteous deeds, Allaah The Almighty will admit him into Paradise and will allow him to marry from the Hoor as He wills.

We are not aware of the Hadeeth mentioned in the question; however, there is a Hadeeth with similar meaning that was reported regarding the prohibition of wine drinking. It was reported that the Prophet, sallallaahu ‘alayhi wa sallam, said that the person who drinks wine in this world will not drink it in the Hereafter, unless he repents. [Muslim and others] This means that the sinner will not be deprived of enjoying the pleasures of Paradise if he repents from his sin. 

Allaah Knows best.