[Phanx]

RaidBossEmoteFrame:ClearAllPoints()
RaidBossEmoteFrame:SetPoint("BOTTOM", RaidWarningFrame, "TOP", 0, 10)

But, keep in mind that the UIErrorsFrame is above the RaidWarningFrame by default, so you may see some overlap unless you move that too.

Alternatively, you could just redirect the messages to the RaidWarningFrame:

local add = RaidNotice_AddMessage
RaidNotice_AddMessage = function(frame, ...)
    if frame == RaidBossEmoteFrame then
        return add(RaidWarningFrame, ...)
    else
        return add(frame, ...)
    end
end