http://www.naics.com/naics-code-description/?code=621340

The code for occupational therapy is 621340.

Is this the code for independent contractors (1099 Employees) Occupational Therapists as well? Thank you in advance!

The code for occupational therapy is 621340.

Yes, but does that apply to independent contractor Occupational Therapists who get cases assigned through an agency and work in clients' homes? I ask because the 1040 instruction classify 621340 as "Offices of physical,
occupational & speech therapists, & audiologists." The work is OT, but it doesn't happen in an Office. Does the same code apply? I know this is splitting hairs, but I want to be sure. Thank you!

Yes, it would still apply.  This code is used for statistical purposes as to "normal" expenses related to the occupation.