Considering a spring vacation to Yellowstone/Jackson Hole/the Tetons,spanning the last week of April and first week in May. Is this too early for the best scenery/wildlife viewing and will lodges/restaurants/hiking/touring be operational at this time?

This is always when we travel to Yellowstone. Late April to early May. Although we do not stay in the park, we do stay in Cooke City (Hoosiers - small but immaculately clean and very nice owners). Also, in Red Lodge (Yodeller - again small but so clean). We have never had a problem travelling the lower roads, even in years of heavy snow fall. It is doubtful that the high passes will be open (I could bet money on it) such as Bearstooth. But you could probably drive up to the first block on Bearstooth and that is quite scenic.

We love going early as it is still cool, there is still some snow but if you are semi accustomed to cold weather, all you should need is a heavy flannel shirt over your regular shirt or a fleece jacket. Be sure to dress with some layers as the sun can be quite hot but the wind cold.

The best thing about that time of year is that you can see tons of wildlife without the huge number of cars and tourists. Prices for the motels are also reasonable then. What we found to be the negative was the poor condition of the roads within the park. Each time we have gone early, there are huge potholes and such that have not yet been repaired. These are mainly caused by frost heaves during the winter. So do be careful when driving within the park that you don't suddenly hit a pot hole that is 8 - 10 inches deep. It is hell on your hubcaps and tires.

Yellowstone Park is open all year long. The wildlife is there all year long. You just have to prepare for the conditions. Likely snow will still be on the ground.

Yellowstone open all year???? depends on your definition of "open"
The only entrance that stays open is North-Mammoth Springs.
Jan.,Feb., March almost all of the facilities are closed. However, there is access to the park for skiing, snowshoe hiking from Mammoth via "snow cats" with advance arrangements.At present snow-mobiles can be used in the park from the north but there petitions being circulated to outlaw them within 3 years.
the closing/opening of roads and facilities is on Yellowstone National Park web site.
Hope this helps

Call the park or check their web site for road openings and closures. The high elevation can create weather patterns that are one of a kind. We once went mid-september and mornings were in the teens with the park roads closed several days because of snow. When it freezes, many roads close simply because the geysers' water cover the roads with heavy ice.

What about Jackson Hole--Grand Tetons--South entrance to Yellowstone about third week in May? There's an airfare sale on that ends May 23. Of course, no one can guarantee nature, but what is your experience?