People say that and it may be true, but if it is, why do so many people turbo VTEC engines? Rumor on the street is that the GSR engine is real friendly to boost. But you can go ahead and believe that a non-vtec turbo is better, but tell that to the people on the HONDATA website. There is a 647 wheel HP LS/VTEC on there. Or talk to HONDA TUNING who had a 10 second daily driver Teggy on the cover, GSR motor with TYPE R crank and head, 600 HP. Oh yeah and almost forgot, FULL-RACE.com who has a Civic Si turbo'd witth 616 WHP. Personally, I'd be pretty damn happy with those numbers.
Ok, sorry about the smart ass part. Now for the more technical part. Basically, the turbo cancels out the VTEC, they don't work against each other. The VTEC and the turbo are both made for top end, hence the reason the turbo cancels out the VTEC. Others argue that the VTEC helps the turbo spool by the fact it opens the exhaust valves for a longer period of time while the non-vtec does not have this feature.
That's the explanation as to how I understand your question when I asked about it.
edit: Yeah forgot something. Another advantage that the LS has over the GSR is the lower compression. But after you build your engine enough your gonna end up getting new pistons anyway. I say go GSR w/ turbo.