It was another example of how central Rooney has become to United's hopes of glory following the departures of Cristiano Ronaldo and Carlos Tevez last summer.
But Dunne knows United have plenty of talent in depth.
He said: "Last year everyone was saying United are relying on Ronaldo too much.
"One man doesn't make a team and, regardless of who's scoring the goals for them, United are still up there and challenging strongly.
"As good as Wayne Rooney is, and he has been in fantastic form, he can't just do it all on his own.
"He needs support, but then the players that they have there will nearly always be the best around."
Dunne, who helped Villa hold Arsenal to a goalless draw in the Premier League on Wednesday night, added: "Would I have preferred to play Manchester City? No, I'm at Aston Villa now and that's all I'm concentrating on.
"For me and for the club, it's going to be a great day at Wembley and that's something we can look forward to.
"Manchester United are one of the biggest clubs in the world so we're looking forward to a tough final against them."
Dunne feels United's players will not dwell on their league defeat to Villa at Old Trafford in December, saying: "The fact we won at their place won't affect Manchester United, I don't think.
"It's more for us. It gives us the belief that we can beat them.
"We've beaten United once this season so we know we can beat them again.
"But, come the big games and the finals, it's United who have all the experience and all the knowledge of playing in them and winning big tournaments."
Dunne is adamant the final in just over a month's time - and their continuing involvement in the FA Cup - will not be a distraction from Villa's aim to qualify for the Champions League.
He said: "I think the target for the team is to finish higher than we did last year. Hopefully that could potentially mean a Champions League spot.
"We just need to make sure between now and February and the next FA Cup game that the league is our bread and butter.
"We have three really tough games coming up in a row and, if we can nick some points out of them, it will kick-start our challenge for the final."
Arsenal boss Arsene Wenger angered Villa boss Martin O'Neill after claiming Villa were a "long-ball" team, but Dunne is adamant the tactics are employed to make the most of the pace of the likes of leading scorer Gabriel Agbonlahor.
He said: "I think everyone is a long-ball team compared to Arsenal. They play so much good football.
"We've got pace in our team up front and that's how you use it.
"They're not just hopeful long kicks forward. They're carefully placed balls that we know our centre forwards can get on the end of because they can outpace most defenders in the league."
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