In theory, the 35S should be acceptable to NCEES. The 33S is OK because it lacks I/O and significant alphanumberic capabilities. I don't see any reason to suppose that the 35S would be any different.
In practice, though, I could see a couple of potential issues.
First, NCEES wants to keep their list of approved models to a minimum, to simplify enforcement. So they might be reluctant to add the 35S to the "approved" list, as long as the 33S is still available.
Second, NCEES is seriously considering a plan to standardize on a single calculator model, and to issue the selected calculator in the exam room. If this occurs, it seems possible that they might prefer to standardize on an "approved" Casio or TI model, given their low cost ($10 - $20) relative to HPs (~ $50 for the 33S, ? for the 35S).
Edited: 30 May 2007, 5:05 p.m.