Hi Anthony,
Looking at the code in "progressbar.m", it might be a little difficult to merge the progressbar figure with your GUI figure but one way of doing it would be to somehow get the handle to the axes for the progressbar figure and make your GUI figure its parent. Alternatively, you can call the progressbar function from your main GUI code but this would display the progressbar figure separately from your GUI figure.
Feel free to ask the same question to the author of “progressbar.m” by commenting directly in File Exchange.
Richa