mysqldump: How to include index type?
You should not worry about embedding the USING BTREE onto the indexes. Why ?
The default index type for MyISAM and InnoDB is BTREE. You cannot impose any other type.
The default index type for MEMORY Storage Engine is HASH. You can impose a BTREE index type.
I wrote a post 4 years ago on HASH not being allowed for MyISAM and InnoDB: Why does MySQL not have hash indices on MyISAM or InnoDB?
In light of this, there is no need to explicitly tack on USING BTREE.
You can look up the CREATE INDEX Documentation to verify default index types per Storage Engine.
UPDATE 2015-09-24 16:23 EDT
Hey Jared, I got a surprise for you. I went Googling around and there is a way to spit out USING BTREE. The option is --compatible=mysql40. I saw it in StackOverflow : MySQL error USING BTREE
Interestingly, there is sort of a bug report on this. You know who submitted it ? A guy named Jared.