According to what I've read at the HTF, it was. With the sheer number of "Forrest Gump" shots they did to put Sisko and the gang into the original TOS footage, it would have cost a lost to recreate them in HD.
I still don't know how Paramount is ever going to be able to release the TMP "Director's Edition" in HD. The CGI house that did the new shots was shuttered several years ago. Very short sighted of Paramount not to pony up the cash for HD renders at the time.