It's safe to store a known value (for checking) next to the actually encrypted values
Yes, it is secure to do this. Any cipher should be secure against known plaintext attacks after all.

However, if you're using RSA then the RSA decryption routine will already throw an exception during the PKCS#1 v1.5 unpadding, so storing the 'lorem ipsum" data is not necessary: the padding already acts as the "lorem ipsum" data.

If you still somehow require "lorem ipsum" for the symmetric encryption (in case Android loses track of the AES key as well) then you might as well use the "lorem ipsum" as Additional Data for the GCM algorithm. This data is included in the authentication tag but not in the ciphertext. If it is constant then you do not have to include it at all.



Note that you may want to use RSA-OAEP or RSA-KEM rather than PKCS#1 to avoid padding related attacks (RSA-OAEP should be directly available in Java / Android and is therefore recommended, but please do check with the KeyStore implementation and the targetted runtimes to be sure).