Shades of Joshua Nkomo and the ZAPU party.
ZAPU was a party mostly comprised of the minority Ndebele people of Matabeleland, but he was a popular figure in the early days of Zimbabwe and a threat to Mugabe's reign, much as is the MDC and Morgan Tsvangirai today.
A "government of national unity" was formed and Nkomo was given a high ranking position in it.
But the result was that ZAPU got co-opted and absorbed by ZANU and Zimbabwe became a one-party state.
By the time of his death, Nkomo was widely regarded as a sell-out.
Had he not made the deal, he may never have gained power, especially with the parties being largely on tribal lines, ZANU being largely Shona and ZAPU being largely Ndebele, with the Shona greatly outnumbering the Ndebele. But he and his followers, with his enormous prestige, would have been a constant opposition-in-being, even had Nkomo been killed or driven into exile.
It is my undertanding that, he allowed ZAPU to be co-optd to end the Gukurahunzi against the Ndebeles. He never had any real power in the ZANU-PF government; he was merely a figurehead that Mugabe could keep under his thumb. Mugabe's threats against the MDC and Tsvangirai are Nkomo/ZAPU redux. The only difference is that Mugabe is now operating from a much weakened position, ecomomically and politically as his country is nearing melt-down.
Whether he is behind the overture to the MDC or not, it indicates that that there are those in ZANU-PF who see him as the liability he is and are seeking to save their own skin. I don't trust any of them (ZANU-PF) for reasons you have pointed out.