To answer your first question. Yes, the Thallus subspecies should be compatible with the calcareum subspecies when comparing the mineral content of the calcified remains.
Also, both subspecies have a similar amount of aluminum. Aluminum is found in almost all sea species as the sea has on average 1.9 micrograms of aluminum per gram of seawater. Aluminum then builds up in sea organism over time.
Supplements made from Lithothamnium sp Thallus should still be safe to eat as only 0.3% of the aluminum a healthy human eats is absorbed in the GI tract and the kidneys effectively eliminate it. If you, however, have reduced kidney function for some reason then it is sensible to limit aluminum intake.