An SCT can be just as good for imaging DSOs than any other design, and usually better. A Newtonian is harder to balance and mount, and a refractor lacks aperture, which is also important unless all you want is wide field.
While it is true that an sct is easier than a newt for the mount to handle, all to often the beginner might fall into the trap of thinking the mount portion of a forked sct is of suitable quality for imaging faint objects. (Ask me how I know.) In fact I believe that for the smaller sct sizes, likely to be someone's first scope, the amount of money sunk into the design by the manufacturer for the mount portion of a forked sct is less than would be appropriate for imaging of faint objects requiring multiminute exposures at the focal length of the sct. That is of course a generalization that isn't going to be true for every case, but with a majority of new users being visual, how could it, in general, be any different? So, yes for given scope spec's, an sct is easier on the mount with respect to stability, but that means little if the beginner planning dso imaging finds that the fork drive is of insufficient quality for successful guiding. And, yes, if high magnification is desired, an sct variety may be the ticket, but the beginner may all too easily make the mistake of thinking an 8" sct will guide well with its standard fork or with a cheap GEM. Besides those issues, I believe the average standard sct (I only have experience with two 8"s and one 9.25") creates more bloated star images than good newts or refractors, even at the center, for the same aperture and magnification. This of course is another aspect of how contrast varies with the scale of object detail, but it definitely has a negative impact on both imaging and visual use.