I think this needs to be broken down into more species specific responses.
If you're wanting to keep the Northern two-lined salamander (Eurycea bislineata) then I could see keeping them at 75'f year round as detrimental. In their habitat, they usually only experience those kind of temps during the hottest parts of the summer and even then it's in short spurts.
Now, if you want to talk about the Southern two-lined salamander (Eurycea cirrigera)then I think it really depends on the animals harvest location. I find that E. cirrigera found here in Virgina are less heat tolerant than ones found in, say, South Carolina.
Eurycea guttolineata is one species that I'll readily recommend for this type of tank. From my observations in the field, this species seems to prefer a temp range of 70-75'f. I went out herping one day this past August for them when the ambient air temp was 102'f. It was 77-82'f under some of the objects I was finding them under. That was one of the best days I ever had looking for them. I also visit these same areas during the fall and winter months when the temps under the objects are in the low to mid 60's and I rarely find E. guttolineata. Mine were kept upstairs in my house where the temps stayed either in the low 70's to upper 70's, depending on the season, for a couple of years. How did they fare? I found larvae in the tank this past spring.
Just my two cents.