Aliases of literal arguments do not show up in the command suggestions for Brigadier. The commands do, however, still work if you use the aliases. I had a little chat on the Discord server with a couple of the devs and found that this is intentional due to polluting the Brigadier command node map. I would recommend either documenting that this is intentional somewhere (the wiki perhaps?), or maybe add an option to enable this functionality explicitly since it has downsides.

Example code: https://pastebin.com/71hT3fSW
Gif of executing the command with suggestions: https://gyazo.com/c78e08a403f6e95194e1574167e70990