Thread:ParaDoxPrimeCadet/@comment-4080775-20150407020708/@comment-25771248-20150407102723

Technically, it was shown rather than stated.

"It appears that each specific space-time technique has its own unique dimensional void that no other technique can access.[5] However, if techniques of different dimensions are similar in nature,  a user can synchronise their respective dimension with the other one to gain access to it. To achieve this feat, however, requires much more chakra.[6]"

Kamui and Kaguya's dimension are similar in nature, so Obito was able to synchronize Kamui to her dimension, creating a portal with extreme chakra cost.

I copied that from the s-t ninjutsu page of narutopedia: the mother site of this wiki.

And if you may remember, Tobi tried to warp Minato into his dimension. He knew he had the FTG, as he was his sensei. What does this tell you? That he probably knew that another s-t ninjutsu can't be accessed by another.