Talked about on the forum a few times. Search "TPMS valve stem" and similar terms.
The thing is that you're putting something that has far more mass than an air cap on the end of a flexible valve stem. You planning to ride a road at FJR nominal speeds? That's going to a significant force on that floppy bit of rubber. If it breaks off at speed you then have to deal with a rapidly deflating tire. Is that a risk you're OK with? Then you wouldn't probably "need" them.
However, most folks that use TPMS (including myself) switched over to the 83 degree aluminum angle valve stems sold by BikeEffects.com forum member Jeff and were careful about alignment of the front stem to not interfere with the brake caliper. Yes, there's some load that's not the same axis as the stem, but I'm personally more trusting of the aluminum stems given the approximate 7 grams of the Garmin TPMS units.