I beleive the X5 tire monitoring is dependant on wheel RPM's mesured from the wheel hub, not sensors on or inside the tire!., so a sealant shouldn't affect the monitoring system, only the balance of the tire if the sealant were to settle into one position, rather than distribute evenly, which is why I advise against using any sealant for an extended period of time.

The more advanced systems like the one I have on my 7 series, to read actual presures, have sensors intergrated into the valve stems themselves and may be damaged by sealant compounds should they ingress into the sensor assembly.

BTW, I picked up a bit of scrap metal no larger than a 3" nail in the side wall of one of my tires a few weeks ago and the shop (Tyrepower Austraila) still repaired it safely and effectively without having to fit a tube., so even if the object is in the side wall it is still legal to repair it in Australia.

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My much loved machines...
1990 E32 BMW 735i - Daley Driver
1983 Okuma LB15 Twin Turret NC turning center - Money Maker!
1985 Suzuki Sierra - Off-road thrasher and mobile shooting platform
1981 HMT NH26 20HP 30" Gap Bed Engine Lathe - Money Maker!
1966 Lancia Flavia 1800 Coupe - Weekend toy
1941 South Bend 9" Model C Workshop Lathe - Antique restoration project.