I would change tile types were it me instead of worrying about the grout type. Glass tile in a shower can be trouble if something drops and breaks one. Don't need broken glass in a shower.

Just check what the tile manufacturers say in regard to the grout type recommendation. The sales person can pull it up easily.

" For glass mosaic tiles, use a specialized translucent epoxy grout that enhances the light and color of the tiles, or a non-sanded grout for smaller grout joints to prevent scratching. Do not use standard sanded grout for delicate glass tiles, as the sand can cause scratching. Epoxy Grout (Recommended for mosaics)

• Why it's best: Epoxy grout is non-porous, highly durable, stain-resistant, and does not require sealing. Translucent epoxy grouts, like Litokol's Starlike or Mapei's Kerapoxy CQ, are ideal for glass mosaics because they refract light and take on the color of the adjacent tiles, creating a seamless, reflective finish that complements the glass artistry.
• Pros: Long-lasting, low maintenance, excellent for high-moisture areas, and preserves the beauty of the glass.
• Cons: Can be more challenging to apply than cementitious grouts and requires careful handling.

Non-Sanded Grout (For smaller joints)

• Why it's used: For glass tiles with small grout joints (1/8 inch or less), a non-sanded grout, like MAPEI Keracolor U, is recommended. The sand in sanded grout can scratch the delicate surface of the glass tile.
• Pros: Easier to install than epoxy and more cost-effective.
• Cons: It is a porous material, so it is susceptible to staining and requires sealing and regular maintenance. "