"X is to be admired" usually means, "I know some people admire this, but I'm about to give a reason than they shouldn't, or shouldn't admire it as much as they do." In English we often call this "damning with faint praise"--i.e., giving a mild compliment that actually constitutes a criticism.
"X is admired" would not be grammatical in this context, although it would be fine in a sentence such as:
Sheila is admired by her friends and coworkers.
You could say, "and that is admirable," which carries approximately the same meaning as "to be admired," but sounds slightly less dismissive.
There are a variety of other phrases you could substitute here for a similar effect--"worthy of praise," "no small accomplishment," etc. What they have in common is that they're wordy and they don't indicate that the speaker is joining in the positive evaluation.