I haven't been to DL in many years, but from what I have read, I'd suggest the
ecv is probably a good idea. DL is more compact and congested than WDW, so it's best if you feel secure in your abilities using the ecv before you get there.
I don't know how many DL attractions have any shaded areas available for waiting, but I'd be willing to bet that not many do. So, a GAC for a shaded place might not really help a lot. You should plan that even if you get a GAC, you probably have to plan that you will be out in the sun a lot, so plan to have things like brimmed hats, sunscreen,
sunscreen clothing, drink a lot of fluids, etc.
There are no special needs I can think of associated with hypertension (other than the attractions that have warnings). If you do request a GAC, you need to be specific about the needs you have, not your diagnosis (because that doesn't tell the CMs what they need to know).
You can also get information from the
DL Guidebook for Guests with Disabilities online at the official Disney site.