It's not a very ugly name, but I find it boring and don't like it, also I guess the reason that it's a bit of a granny/elderly auntie name is a turn off for me. I also don't think it's particularly classy, and I usually like more classy, or even sophisticated names. I know a few Jolantas that are pretty okay and very kind and likeable ladies, and I find the nickname Jola slightly better than the full name.
Some common nicknames are Jola and Jolka, also Jolcia, Joleczka. This name is quite popular among women born in the 40's-60's, perhaps early seventies, but is rather dated now, I know one Jolanta (Jola) who was born in the early 90's though, and I know one toddler with the middle name Jolanta, but the latter is after a relative, but overall it seems to be out of favour nowadays. Last year there were 25 girls born who were given this name. You can call it vintage I guess. :D Although for some people it has a bit of a comedic feel, don't know exactly why really, although I myself can't say I like it.
It's surely more accurate than yo-LAHN-ta. According to this site's key "o" is pronounced as in the word "boat" which isn't how Poles pronounce the letter "o". While "aw" is pronounced as in word "bought" which sounds much more like the Polish "o".