Gerbick, not really. They changed the spelling rules a few years ago, and according to the new spelling (which I don't use because it's not logical ...), you use the 'ß' in fewer cases than before. It's still there, though, and it's a spelling mistake if you use 'ss' where 'ß' should be used.

You're right that ae/oe/ue are accepted workarounds for ä/ö/ü when you don't habe the respective umlauts on your keyboard (or need to write plain ASCII). The same way, 'ss' is used to replace 'ß'. - The problem with these approaches is that while it's readable, it looks clumsy and unprofessional. So if you have any chance to avoid these workarounds, do it.

(Plus: While 'ae' instead of 'ä' will always be recognized as "the person did not have 'ä' on his/her keyboard", 'ss' instead of 'ß' may be mistaken as a spelling mistake if there's not enough context around to make it clear it was used on purpose. So... one more reason to do it right.)