關於 "permanent" in employment verification letter

I-485 application:
Here is an example from my lawyer:

Dr. xxx is currently working for us as a _____________. His employment with us began in _______________, and is expected to continue on a full-time permanent basis. For Dr. xxx’s skills and services, he is remunerated at an annual salary of $_______________.

我的問題是：
1. 老公所在公司拒絕 “permanent" 一詞，理由是所有的工作都是"at will". 如果去掉"permanent"一詞，行嗎？ 我們律師說不行。類別： NIW.

2. 我是F-1 （research assistant), 是否也需要 employment verification letter？一樣的版本嗎？

謝謝