Basically yes, an antenna converts electromagnetic waves (radio waves) into a voltage when receiving but it also works in reverse, applying a voltage makes then create electromagnetic waves. If you connect two antennas back to back, excepting that there will be some signal loss because they are not 100% efficient, the signal gets coupled from one to the other. The one inside the can picks up the TPMS signal and the one outside radiates to to the ECU's receiver.
Coax is a shortened name from "concentric-axial", meaning "in line with one inside the other". It is a kind of cable with an inner wire suspended centrally in some insulation and inside an outer screen sheath. I suggest semi-rigid cable because the insulation is normally solid but flexible plastic so it is air tight. Electrically, the coax cable used for example on TV antennas would work equally well but it usually has a cellular construction which would allow air to escape. That would make it difficult to pressurize the canister. You can solder to the outside of semi-rigid coax but you can't easily solder to aluminum so I would recommend forming it to shape then using epoxy resin to seal the hole.
There is an entirely different approach to this problem which you should consider but it takes some programming skill: The TPMS units as basically a timer that wakes them up every few minutes, a pressure sensor and a low power radio transmitter. You can make a small unit that mimics the TPMS signals and fools the ECU into thinking it sees real data. You only need one unit, it can mimic all the TPMS senders by sending fake information in sequence. I haven't done this myself but it isn't technically difficult, I can read my own cars TPMS on a radio receiver here (we use 433.92MHz in Europe) and it is just a stream of numbers, if I copied good data and kept resending it the ECU would be none the wiser, even if the wheels were completely removed! I'm thinking of something small enough to fit inside a tiny box or a USB stick enclosure.
Brian.