sure its ok to tell a therapist you care about them....here in NY this kind of thing is called attachment not transference, unless the feelings towards the therapist is one where a person is feeling that way because they feel that way for someone else...

example here where I live and work If I like/care about my therapist for no other reason then I like my therapist for who she is and how she does things its attachment, if I like/care about my therapist because I am transferring my love for my wife to my therapist then its transference.

whether its transference or attachment here where I live and work it is ok to tell a therapist when you like, care, love them and would like to have an outside of therapy relationship. NY is one of the USA states that does allow for friendships after a client and therapist no longer have a business relationship.

you can find out if your location allows for this kind of thing by talking with your treatment providers or by contacting what ever agency over sees mental health ethics in your location.