As A Something

Yes it is grammatically correct.

a. "His getting to work on time is evidence of his commitment."
b. "He gets to work on time as evidence of his commitment."

I have a feeling that b) is not quite right because of a). The underlined part of b) is not the same clause type as the underlined part of a).

Getting to work on time is every employee's unspoken contract with his employer. I don't think we can call it a commitment.

Let me make a slight change:

a. "His getting to work earlier than necessary is evidence of his commitment."
b. "He gets to work earlier than necessary as evidence of his commitment."

I have a feeling that b) is not quite right because of a). The underlined part of b) is not the same clause type as the underlined part of a).

They are both fine, but A is the speaker's observation while B states the worker's intention.

How do I interpret this:

c. "He came home nightly as evidence of his late-night partying."

Does it mean he intentional came home late every night to prove after the fact his partying intention?