The group was dispersed from its base at section 111 at Celtic Park back in December following numerous complaints about behaviour.
The runaway Scottish Premiership leaders were fined £42,000 by UEFA after a huge banner depicting IRA terrorist Bobby Sands was unfurled during a Champions League clash with AC Milan on November 26, while the ultras were also blamed for damage to seating at Fir Park a week later.
But a 250-strong band of supporters, including two drummers, who carried with them a huge Green Brigade flag marched into section 118 of the Lisbon Lions Stand five minutes before the Hoops kicked-off their 3-0 win over St Johnstone.
A Celtic spokeswoman refused to confirm whether the group would be welcomed back permanently, saying only: "They were not banned and they bought individual match tickets."
But Lennon - whose side won courtesy of an Anthony Stokes hat-trick - would welcome their return.
He said: "Whoever they were - I don't know if they were the official Green Brigade or not - I can't thank them enough because they made a hell of a difference to the atmosphere today. The players would have thrived on it.
"I got word this week that they might be in and I was delighted to hear that noise. You tell even just by the rhythm of the game that they added to it.
"So long as everyone works within the rules of the club then we welcome that colour, energy, noise. It's been part of my time here for the last three and a half years and we don't want to miss that because they brought a lot of good to the ground.
Lennon handed Leigh Griffiths his first start since securing a £1million switch from Wolves a fortnight ago and watched as the former Hibernian man teed up Stokes for the 16th-minute opener.
The Irishman wriggled past a couple of half-hearted challenges before planting the ball beyond Alan Mannus in the Saints goal.
Scott Brown then scooped a cross to the back post for Stokes to bury his second on 64 minutes, while his treble was complete two minutes later as he smashed the ball beyond Mannus again after Stefan Johansen and Kris Commons combined down the left.
The victory also saw Fraser Forster rack up his 12th league shut-out in a row to equal the 43-year-old record set by former Aberdeen goalkeeper Bobby Clark. The England keeper now has to survive just 31 minutes against Hearts at Tynecastle next Saturday to beat Clark's record of 1,155 minutes without conceding a league goal.
"He can be really proud of what he is doing at the minute," said Lennon. "It means a lot to him personally. He's got 31 minutes to go and these are great incentives for the players, not just to win the title, but to win it in a certain style.
"He's a fantastic goalkeeper. He's one of the best Celtic have ever had. For him to achieve what he has achieved in such a short space of time, I think, is miraculous."
Celtic reaffirmed their 21-point lead over Aberdeen with the win to put them on the verge of three-in-a-row.
But their manager was unhappy with morning headlines which suggested he may be about to quit his post.
"I don't know where they came from," he said. "I was asked 'Do you think you have taken the club as far as you can?' and I said well maybe the last 16 is maybe as far as we can go for the time being, so I think it was taken completely out of context.
"I hope I will be here for the long haul. I haven't changed my mind on anything. I've got work to do here."
St Johnstone boss Tommy Wright refused to criticise his players for losing to the unbeaten Parkhead men.
"I thought Celtic were excellent, they played very well and kept the ball, " he said. "They would have been hurting from losing to Aberdeen last week so it was no surprise that they played so well.
"I'm not going to criticise my players coming up against a team like that. We had started okay but ended up chasing the game. But Celtic were fantastic today."