Hearsay can't be used to establish fact, but it can be used to present the possibility of an alternative scenario from what the prosecution is presenting. It would carry less weight but should still be admissible.
An example would be the Caylee Anthony case, where the defence presented an alternative scenario without any evidence at all, other than implied hearsay. As I said, the bar is lower for the defence, they do not have to prove what they say, it just has to be a plausible alternative. The defence can deal in doubt, but the prosecution cannot since the burden of proof is on them. The main limit on the defence is that they can't present something as fact which is provably false, since the prosecution will do that if they can. In the case of SA and DA, both men apparently placed themselves at the scene in some fashion, that remains a fact irrespective of what they actually said and how reliable it might be, and is independent of the statements themselves. Perhaps details they provided might not be accurate and can be proved as such, but by their own free admission they were there. So, the details of their actual statements are less important than that fact, and their statements can be used for that purpose. The defense does not have to prove that SA and DA did do the crime, but only show that reasonably they could have done the crime. And their statements, as inaccurate and as unreliable as they might be, show that. The argument will be that they made these statements to hide or minimize their personal involvement, and that the crime was entirely their doing. The defence will argue that in fact JA and ZA had nothing to do with the crime, and their only role was as convenient patsies because of their local notoriety.
The only way for the state to get around that would be to present forensic evidence or independent witnesses directly implicating the accused. Otherwise the only people with an undisputed link to the crime are SA and DA, and a fair jury would have to acquit the other two.
