Thats not true. The "Grote tanks" (the monster tank projects designed by Edward F. Grote) were rejected by Waffenprüfamt 6 and Speer in late 1942 before they got any attention by other persons. The tanks like the Ratte or P.1000/1500 are pure paper designs never intended for production.
Source: Überschwere Panzerprojekte: Konzepte und Entwürfe der Wehrmacht by Michael Fröhlich
So they are pure fake
I never talked about the Grote tanks and of course I have read Frohlich's work.
I mentioned specifically Ratte, which got a direct approval from Hitler and later, as you said, was vetoed by non other than Speer himself.
He says so in his first memoir "Inside the Third Reich", if you really want I will give you page number when I get home.
But now that you mentioned Grote, I have to say, that he generally is the epitome of a sketchy figure in history in general. Few, if any, fragments of his life and work survive.
What is known about him is that he was born around 1884. What did he study? What did he learn from early years? Nobody knows. He appears in WW2 history in 1929/30 when he was working in Rheinmetall
and got an invite from the Soviet Union to try and set the foundations for a mechanological industry. His first monster paper tank was designed in 1930 and was named TG (Tank Grote) which did not fight in any war.
Under undisclosed conditions, he left USSR in 1933, where it is unknown what he was doing. In 1941 he worked in the Ministry of Armaments (under Todt back then) where he was assigned as a field tester for the naval division. What he did is unknown (at least to me).
How he came across as Hitler's pet project designer is unknown. What is more unknown is the profile of another mechanic called Hacker. Both of them got hired by Hitler for the top secret project of the Landcruiser P1000 "Ratte" and P1500 "Monster" (Fortress Tanks were envisioned to be the future).
In 1942 Speer vetoed it.
The rest of his life is completely unknown. The last surviving piece of himself is an application dated April 1950 for a patent in West Germany (patent for what? nobody knows). According to the document, he was living in South Africa at the time.
Truly a shadow figure if there ever was one in WW2 terms.