no you don't have to be in safe mode to do it on x64 win 7.. you can but not necessary.
first.. yes the latest version does work on win7 and on ff14.
read their forums. they reply fast and the mods/admins are very helpful and nice but search the forum for answers first cause they are there.
Their forums and wiki are very helpful but here is the wiki link that explains how to install everything and about the x64 bit driver process that doesn't involve safe mode:
http://www.motioninjoy.com/wiki/en/install
you'll see the 64-bit and disabling Driver Signature Enforcement link.
Also use the version 5 link info for version 6.. they haven't posted v6 info.. probably cause it's same thing as ver.5.
their site is http://www.motioninjoy.com/
I was able to get my ps3 controller to work with rumble just fine on ff14 win7 x64 but now I use a plain jane Logitech controller. no rumble but I don't have to mess with motionjoy and all that other bs. I just plug it in, use the ffxiv config to set it up and works great.
logitech does have rumble cheap controllers that might work.. haven't tested 'em.