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Als not a favourite of the period. Most blue tourmalines are Paraiba tourmalines, which were only discovered in the late 20th century.

Yes it would, at least to see if it is glass or stone.
And look at what Charles Horner used. In spite of the recognizable CH swirl designs, they used gemstones their other Western European colleagues used at the time. They also used enamel and glass, also very Art Nouveau.

 

Yup - they used what looked good and what was to hand. Indicolite tourmalines have been around for a long time, in use since the early 1800s I think, but from what I saw tend to be pricy. Paraibas are another thing and IIRC were discovered post-WWII. Glass in this case might be the safe bet.