Yeah, I have that book (Grey Wolf). It is possible, so much went undocumented as the Reich fell apart, but I remain unconvinced.
I am also very skeptical about Russian claims that they recovered his body at all.
The skull fragments have been proven to be not Hitler's. DNA testing revealed them to be that of a woman but not Eva Braun's.
So, once again, the Russians lie through their teeth about everything.
I think that's all true, but that the explanations are as much explainable by the mundane as the malevolent.
Soviet soldiers show up at the Chancellery with orders to get his body. But the SS has (perfectly logically) burned his body precisely do the Red Army can't parade/display it, or
even reliably identify it. No DNA testing at that point, right?
So the soldiers/commisars can either 1) tell their superiors they can't find/identify the body, which could lead to rumors that Hitler may have escaped, claims the Soviets "failed to get Hitler", and allegations of incompetence on the part of the soldiers at the Chancellery, etc., or 2) they grab whatever ashy, messy, burnt remains they can, claim "we got him", and bring those remains to their superiors. Of course, those superiors have the same incentives -- nobody wants to tell Uncle Joe that they're not sure, or may not have the right bodies. So they too claim "we got him".
From that point, those remains get buried and moved a few times, and I can just picture the real world scenario when the next unlucky sap is directed to go get them. There's nothing really identifiable, and no way of knowing that they have the right stuff, but nobody wants to be the one to admit that. So, the façade continues. And when they're eventually tested after DNA tests are available, they don't match.
I don't think that requires a true "conspiracy", or supports an idea that Hitler really survived. I think there's a ton of reasons why his survival is/was impossible as a practical matter. The truth is that the SS were successful in accomplish their goal of destroying the body so that it could not be reliably recovered, identified, and paraded in triumph. It's really as simple as that.