I'd say that it is pretty difficult, although not impossible, to be drafted from a HA D3 school. There were six players drafted from D3s last year and not all of those were HA schools.
https://www.d3baseball.com/not...fted#google_vignette
There were 14 drafted from DII programs:
https://www.ncaa.com/news/base...ected-2023-mlb-draft
There were 44 from JUCOs and about 123 (I think) drafted out of high school:
https://www.mlb.com/news/facts...(Round%2013%2C%20No.
There are 600 spots, so that leaves 413 drafted out of D1 College programs.
As for the summer, even good D1 players often have a hard time getting into great summer leagues, especially since the recruiting for those teams starts even before the spring season. Some Cape players are committed from mid-August of the summer before.
I think if your player wants to go the HA route and be drafted, he might prefer a D1 school where he gets to play a lot-- the school doesn't have to be a D1 powerhouse school so long as he gets to play. Even the Ivy League competes down south in the spring, so there is always a chance to be followed from a good outing against a great baseball school during the preseason.
Also, what about the student part of the student-athlete equation? Your player could be the absolute best student at his JUCO and get lots of transfer opportunities. But sometimes those credits won't articulate directly into a HA four-year program, and it may take the student another year to complete at a four-year after his JUCO degree, making him responsible for five years of college tuition. These decisions are very individual and hypotheticals often can't answer the question out of context.