First, I have to state that I have absoloutely NO hands-on knowledge about the bladders..........Now.
A big "rubber" sack, lining a metal tank...presumably the openings for fill and demand are both clamped/gasketted/bonded to the openings in the metal tank.
These bladders are (if they're fit for purpose) strong enough that the metal tank can be severely deformed/distorted, yet the bladder will retain it's integrity with a large weight of fuel sloshing around in itand possible gross misalignment between inlet and outlet.
Anyone want to "flame " that hypothesis?
So why all this paranoia about dipsticks?....the bladder spreads away from the filler and is impossible to "use" to empty,-therefore there is a layer of fuel ALWAYS spreading the bottom and thus the lower-sides.
If Robbo were doing the job properly, there would be a bonded-on "crash-plate" beneath a guide-tube so the dipstick has only one direction to go and could not puncture the base..
A properly-designed dipstick would have a cross-piece or flange at the "handle" end so it wouldn't touch the bottom,anyway.
A bladder that's strong-enough to meet the service-requirements is unlikely to be damaged by a non-metallic dipstick dropping under it's own weight.
One would hope a Rotary pilot would have the intelligence to refrain from having at it like Dartagnan
the smooth, rounded tip should make penetration impossible anyway.
As a former petrol Retailer, I've dipped a lot of Motor-Spirit, Kero and Diesel tanks,taken deliveries and checked the tanker-dips and drained tanks!
So, my advice is to examine objectively and dip intelligently!