Using tags in Custom Recipes work, Custom Block Tags work too with commands. But once you try to use a custom block tag inside a custom recipe the game can't find it.

{
"type":"crafting_shaped",
"pattern":"###",
"key":{
"#":

},
"result":

}

Causes exception:

[13:12:54] [Server thread/ERROR]: Parsing error loading recipe madcustom:shapedtesthoriz
com.google.gson.JsonSyntaxException: Unknown item tag 'madcustom:stonealike'
at aor.a(SourceFile:180) ~[minecraft_server.17w50a.jar:?]
at aor.a(SourceFile:149) ~[minecraft_server.17w50a.jar:?]
at aoz.c(SourceFile:229) ~[minecraft_server.17w50a.jar:?]
at aoz.b(SourceFile:23) ~[minecraft_server.17w50a.jar:?]
at aoz$a.b(SourceFile:253) ~[minecraft_server.17w50a.jar:?]
at aoz$a.a(SourceFile:248) ~[minecraft_server.17w50a.jar:?]
at aox.a(SourceFile:47) ~[minecraft_server.17w50a.jar:?]
at aov.a(SourceFile:52) [minecraft_server.17w50a.jar:?]
at sk.c(SourceFile:132) [minecraft_server.17w50a.jar:?]
at sk.a(SourceFile:115) [minecraft_server.17w50a.jar:?]
at net.minecraft.server.MinecraftServer.a(SourceFile:1308) [minecraft_server.17w50a.jar:?]
at net.minecraft.server.MinecraftServer.a(SourceFile:334) [minecraft_server.17w50a.jar:?]
at net.minecraft.server.MinecraftServer.a(SourceFile:280) [minecraft_server.17w50a.jar:?]
at qe.d(SourceFile:235) [minecraft_server.17w50a.jar:?]
at net.minecraft.server.MinecraftServer.run(SourceFile:467) [minecraft_server.17w50a.jar:?]
at java.lang.Thread.run(Unknown Source) [?:1.8.0_144]