It was essentially a jigsaw puzzle, and Venters insight was that computational power was just as important to the project as biology. The Human Genome Project was essentially trying to sequence the human genome by finding large chunks of DNA and fitting them together like a jigsaw, finding which bits unambiguously matched up.

Venters idea was that you could do the same with small chunks of DNA, if you approached it as a computational problem and used computers to try/evaluate/reject the millions of ways the pieces could be fit together. So he recruited mathematicians, computer scientists etc and got them to work on the problem. He speeded the project up massively by making the biology bits simpler (smaller pieces of DNA) and shifting the effort to the computational problem.

So he made a big difference. And his insight that it was a computational problem is kindof obvious now but it wasn't obvious 25 years ago.

https://en.wikipedia.org/wiki/Shotgun_sequencing

Involved in the sense that his method worked and the one the Human Genome Project insisted on didn't. In the end, they had to use his method to catch up enough that everybody could pretend they did it together and collaboratively -- even though Venter clearly got there first. Venter deserved a Nobel Prize for that and, quite frankly, the Human Genome Project guys deserved a firing.