Lens is really cool but sadly it depends on ghci being available which immediately breaks ARM compatibility. :(
Do you mean Template Haskell? If so, I'm pretty sure it's not required for use, just to have the lenses defined for you. You can still define them manually, at the cost of a little extra boilerplate.
If you actually mean ghci, then I have no idea what you're talking about...
EDIT: And this link ties Template Haskell to GHCi: http://stackoverflow.com/a/10929803
Maybe what you're thinking of is the problem with cross-compiling and Template Haskell. Generally speaking, that does not work because Template Haskell can do evil platform-specific things at compile time, so if the host and target architectures don't match, you can run into problems.
Anyway, you can use Template Haskell on ARM, you just have to compile it on ARM.