In your specific example, yes it is possible.
HTTPS starts a TLS session with the remote.
TLSv1 Client Hello
Secure RDP starts an RDP session that negotiates a TLS secured connection between the two ends of the session.
X.224 Connection Request (0xe0)
Because the session-start protocols are different, a stateful firewall should be able to discriminate between an HTTPS connection starting up and something else.
For the generic case, a Firewall won't be able to detect something like SSH-over-HTTPS since the SSH traffic is hidden inside the HTTPS traffic. The only way it could detect it is through heuristic analysis of the traffic patterns, but I don't know of anything that does that.
For IMAP, there are two modes of securing it. One is via SSL, another is via TLS. The SSL method looks just like an HTTPS connection just on a different port, and if the remote port is the same then there isn't much it can do about it. TLS, on the other hand, is negotiated between both ends of the conversation so the session-startup is markedly different and easily detected.
The key thing to keep in mind is that SSL creates a TCP wrapper through which traffic is passed. Many protocols include a method of negotiated security inside the protocol itself that leverages much the same technologies the wrapper uses, but uses a different session startup method which makes it differentiable.