I'll call that a steaming pile of bovine excrements.
First of all both normal queues and ranked queues have their own MMR for each player.
Secondly, both blind pick and draft pick have their own separate MMR.
Thirdly, every map has it's own separate MMR. (which is irrelevant here, but I thought you'd want to know)
Now to the main event.
Not only Teambuilder had it's very own separate MMR, it also accounted for each and every single individual champion you played separately. Moreso, it was also giving you "leg-up" for your first few games.
Of course the system can widen the ELO range for matchmaking purposes, but ONLY within the same queue.
Should there be a situation where there is only one person in solo ranked Plat and it's Plat 3 on the server they could be matched with Diamond or Gold from solo ranked, but ONLY from solo ranked.
It will never use team ranked or normal MMR to find player.
NEVER.