No. Premiere Elements 12 does not support third-party plug-ins.
In very general terms, I agree with Steve, however, there are some VST's, that PrE can use for Audio - just not nearly as many as PrPro, or Adobe Audition (or any number of other audio editors). I do not know about Isotope Nectar, specifically though. PrE is extremely limited, as to which VST's it can use.
Also, having some VST's on one's system, can cause Premiere to not launch, and they must be "hidden" from Premiere. This Tips & Tricks article goes into more detail on VST's. It covers VST's in Premiere (both Elements and Pro), but is geared more toward PrPro: http://forums.adobe.com/message/3077222#3077222
Provided that the existance of Isotope Nectar on the computer, does not stop PrE from launching, it would be easy to check, as to whether PrE can use it - if it appears in the Audio Effects, then it can be used. If it does not, then it cannot. Because some VST's cause that program launch failure with Premiere, many users have issues, trying to run it on a DAW.
So, the answer is probably not, but that particular VST might be one of the exceptions? I have a couple of EQ VST's, that work in both PrE and PrPro, some others that only show in PrPro, and not PrE, then a bunch that all work fine in Audition, and a few other audio editing programs - it is a "crap-shoot." Fortunately, I do not have any that cause failure to launch with either version of Premiere.
Thanks for taking out the time to answer.