Should be ok with a GTR bonnet.
You might need the GTR hinges and the bonnet latch as the GTR bonnet
sits higher due to the top of the front bar sitting higher.
But having said that, the East Bear front bar might not sit as high as the GTR (the top of the grill) so you might not need the hinge and latch.
The photo you've posted is actually an add on to the stock front bars.
http://www.east-bear.co.jp/aeroparts/m-piece/R34tp.html
This is a complete new front bar
http://www.east-bear.co.jp/aeroparts/m-piece/R34gts-r.html
You might be better off to get a genuine GTR front bar + the nismo bonnet you want with GTR hinges and bonnet latch.
NB: If you use the genuine GTR front bar it will extend a few mm's past the wheel arch. Not out but back, like towards the tyres if you know what I mean.