To address the last question first: Programming skills are not worth much without some domain-specific knowledge. The latter is what is documented by getting a degree so unless you manage to get an outstanding reputation as a knowledgeable person in some area, it would be best to get a degree.

There is quite a variety of bioinformatics jobs out there so maybe you could precise what kind of job you have in mind.

If a person has pretty reputable programming knowledge, is there need to get a graduate degree?

To find an industry job, no. Keep in mind that your long term job prospects may be limited in that case. A graduate degree would get you climbing the corporate ladder quickly or you could move sideways into marketing etc over time. In academia without a graduate degree you would definitely run into some wall sooner than later.

Historical advice, from oldest to newest (this list is not comprehensive, there are many threads left behind):

Bioinformatics Career In Us And Gemany

Economics Of A Career In Bioinformatics

Will A Masters In Bioinformatics Help Me In Getting A Job?

Career In Bioinformatics

Exploring possibility of career switch to bioinformatics

career for bioinformatics in USA . are there any job opportunities for a student who have completed his/her masters in bioinformatics ?

Bioinformatics Career plans and developments

Advice for someone considering bioinformatics?

Starting a career in Bioinformatics

Majors for a career in Bioinformatics

What's the recommended graduate educational path for a fullstack developer to transition into bioinformatics?

How should i start my career in bioinformatics???

Career in Bioinformatics

If you get into bioinformatics, you may end up like me, i.e., where there is so much interesting and diverse data to analyse such that you don't even want (or need) a permanent job.

The field needs more bioinformaticians with PhD-level skills.