No, I would not recommend feeding alfalfa hay. Somewhat limited(not free fed), good quality alfalfa pellets is plenty for the protein and nutrients a growing bunny needs. Then a grass hay like timothy free fed, for the indigestible fiber to help keep that digestion moving well, which is an essential component for a rabbit of any age to stay healthy. The diet the breeder is feeding sounds fine, provided the bunny has healthy poop, maintains a healthy weight/body condition while growing, and is eating a good size pile of the timothy hay.
In some cases alfalfa hay may be necessary or needed, like with a nursing doe who can use the extra calcium, protein, and nutrients, and needs so much extra food to help support nursing those babies and stay healthy herself. But in most cases, it's completely unnecessary and can actually cause problems.
Like excess uneaten cecals because the rabbit is getting too much protein and extra nutrients and not enough fiber. Or potential bladder issues because of the excess calcium in alfalfa hay being excreted in the urine. Then there are the behavioral issues, that it can make for an extremely picky bun when it comes to hay eating. And when your bun is an adult and you have to stop the alfalfa and switch to a grass hay, good luck with that! They tend to throw a huge fuss and refuse to eat the grass hay because alfalfa hay tastes so much better
So limited alfalfa based pellet and free fed good quality grass hay. That's what I've done, what I did with the litter I last raised, and what I would recommend. A tint bit of alfalfa hay as a treat usually won't hurt if you want, but I would stick primarily to a grass hay, making sure your bun is always eating it well, at least a pile the size of their body per day.
And just a note, with any new bunny, it's recommended to stick with their exact same diet for the first couple weeks they are with you, provided it's not causing serious health concerns and they are doing well. That means, the same brand and type of pellets, and the same hay. And if they are already used to eating veg/greens, the same ones of those.
If the breeder only gives you enough feed for a couple weeks and you can't buy more of the same, then as long as your bun has settled in ok, it's usually fine to very gradually start the pellet transition at the start, so that at the end of the second week with you, they have transitioned completely over to the pellet you intend to keep feeding them. But you do have to make sure the transition is done gradually, and that they are actually eating the new pellet you're transitioning them onto. You also need to make sure it's not causing any digestive issues. It is better to wait two weeks before transitioning pellets, but sometimes that's not always possible.
Baby rabbit diet
https://rabbitsindoors.weebly.com/bringing-your-rabbit-home.html
