Yes, whether you have approved or pending I-751, if you're applying based on marriage to US citizen for 3 years, you need to bring marital evidence and be ready to prove your bonafide marriage.
Some people never had 2 year GC. Then entered the US, received their 10 year unconditional GC because they were married for 2+ years. But if they apply under 3 year rule, they'll have to prove marriage.